Radiation-curable optical glass fiber coating compositions, coated optical glass fibers, and optical glass fiber assemblies

ABSTRACT

Optical fiber coatings are disclosed having excellent ribbon stripping and adhesion behavior. The coatings are radiation-curable. The excellent stripping and adhesion behavior can be achieved by several means which include by use of additives, by use of radiation-curable oligomers having higher molecular weight, or by use of coatings having certain thermal properties. Combination of means can be employed. Stripping behavior can be measured by crack propagation and fiber friction measurements.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application U.S. patentapplication Ser. No. 09/838,140, filed Apr. 20, 2001 (now U.S. Pat. No.6,339,666), which is itself a continuation of U.S. patent applicationSer. No. 09/035,771, filed on Mar. 6, 1998 (now U.S. Pat. No.6,298,189), which is itself a continuation-in-part application of U.S.patent application Ser. No. 08/877,585, filed on Jun. 17, 1997(abandoned), which is itself a continuation-in-part application of U.S.patent application Ser. No. 08/840,893, filed on Apr. 17, 1997(abandoned), which is itself a continuation-in-part application of U.S.patent application Ser. No. 08/745,790, filed on Nov. 8, 1996(abandoned), all of which are hereby incorporated in their entirety byreference.

FIELD OF THE INVENTION

The invention relates to radiation-curable inner and outer primaryoptical glass fiber coating compositions. The invention also relates tocoated optical glass fibers and optical glass fiber assemblies. Moreparticularly, the invention relates to a ribbon assembly having improvedribbon stripping capabilities.

BACKGROUND OF THE INVENTION

Optical glass fibers are usually coated with two superposedradiation-cured coatings, which together form a primary coating. Thecoating which contacts the glass surface is called the inner primarycoating and the overlaying coating is called the outer primary coating.

The inner primary coating is usually a soft coating having a low glasstransition temperature (hereinafter “Tg”), to provide resistance tomicrobending. Microbending can lead to attenuation of the signaltransmission capability of the coated optical glass fiber and istherefore undesirable. The outer primary coating is typically a hardercoating providing desired resistance to handling forces, such as thoseencountered when the coated fiber is cabled.

For the purpose of multi-channel transmission, optical glass fiberassemblies containing a plurality of coated optical fibers have beenused. Examples of optical glass fiber assemblies include ribbonassemblies and cables. A typical optical glass fiber assembly is made ofa plurality of coated optical glass fibers which are bonded together ina matrix material. For example, the matrix material can encase theoptical glass fibers, or the matrix material can edge-bond the opticalglass fibers together.

Optical glass fiber assemblies provide a modular design which simplifiesthe construction, installation and maintenance of optical glass fibersby eliminating the need to handle individual optical glass fibers.

Coated optical glass fibers for use in optical glass fiber assembliesare usually coated with an outer colored layer, called an ink coating,or alternatively a colorant is added to the outer primary coating tofacilitate identification of the individual coated optical glass fibers.Such ink coatings and colored outer primary coatings are well known inthe art. Thus, the matrix material which binds the coated optical glassfibers together contacts the outer ink layer if present, or the coloredouter primary coating.

When a single optical glass fiber of the assembly is to be fusionconnected with another optical glass fiber, or with a connector, an endpart of the matrix layer can be removed to separate each of the opticalglass fibers.

Desirably, the primary coatings on the coated optical glass fibers, andthe ink coating if present, are removed simultaneously with the matrixmaterial to provide bare portions on the surface of the optical glassfibers (hereinafter referred to as “ribbon stripping”). In ribbonstripping, the matrix material, primary coatings, and ink coating, aredesirably removed as a cohesive unit to provide a clean, bare opticalglass fiber which is substantially free of residue. This residue caninterfere with the optical glass fiber ribbon mass fusion splicingoperation, and therefore usually must be removed by wiping prior tosplicing. However, the step of removing the residue can cause abrasionsites on the bare optical glass fiber, thus compromising the strength ofthe connection. The superior stripping functionality of ribbonassemblies to provide clean, residue-free, bare optical glass fibersduring ribbon stripping according to this invention has heretofore beenbelieved to be unobtainable.

A common method for practicing ribbon stripping at a terminus of theribbon assembly is to use a heated stripping tool. Such a tool consistsof two plates provided with heating means for heating the plates toabout 90 to about 120 C. An end section of the ribbon assembly ispinched between the two heated plates and the heat of the tool softensthe matrix material and the primary coatings on the individual opticalglass fiber. The heat-softened matrix material and heat-softened primarycoatings present on the individual optical glass fibers can then beremoved to provide bare optical glass fiber ends, at which the fusionconnections can be made. A knife cut is often used to initiate a breakin the matrix material to the inner primary coating. Typically, onlyabout a 1 to 4 cm section of the matrix material and coatings on theoptical glass fibers need be removed. Identification of the bareindividual optical glass fibers achieved by tracing back along the bareoptical fiber until the ink coating or colored outer primary coating isseen.

U.S. Pat. No. 5,373,578 discloses a ribbon assembly containing aplurality of coated optical glass fibers. Each of the optical glassfibers is coated with an inner primary coating which is adjacent to theoptical glass fiber, with an outer primary coating and an ink coating onthe outer primary coating. The inner primary coating is modified so thatadhesion between the inner primary coating and the optical glass fiberis reduced. This reduction in adhesion facilitates easy removal of theheat-softened primary coating when using a heat stripping method. Whilethis patent discloses, at column 5, lines 10-13, that the adhesionbetween the inner primary coating and the optical glass fiber should besufficient to prevent delamination of the inner primary coating from theoptical glass fiber, any reduction in the adhesion between the innerprimary coating and the optical glass fiber increases the possibility ofsuch undesirable delamination, especially in the presence of moisture.Delamination of the inner primary coating from the optical glass fibercan lead to degraded strength of the optical glass fiber as well assignal transmission attenuation disadvantages.

Published European patent application 0262340 discloses a ribbon cablehaving a “peel layer” as the outermost coating layer on each of opticalglass fibers contained within the ribbon cable. During ribbon stripping,the peel layer is destroyed and the matrix material is removed from thecoated optical glass fibers. However, after ribbon stripping, theoptical glass fibers are still coated with the primary coatings. Thatis, the primary coatings are not simultaneously removed with the matrixmaterial in the ribbon assemblies disclosed in this publication.

U.S. Pat. No. 5,011,260 discloses a ribbon cable having a “decouplinglayer” disposed between the coated optical glass fibers and the matrixmaterial. In this manner, the matrix material may be easily removed fromthe coated optical glass fibers by application of low stripping force.This patent includes a general statement that the coatings on theoptical glass fiber can be simultaneously removed with the matrixmaterial during ribbon stripping. However, this patent fails to teachhow to solve the problems associated with the residues remaining on thebare optical glass fibers after ribbon stripping conventional ribbonassemblies.

Published European patent application 0407004 discloses a ribbon cablecontaining a matrix material having sufficient adhesion to the inkcoated optical glass fibers to remain adhered thereto during normal usebut is easily strippable therefrom without damaging the integrity of theink layer on the coated optical glass fibers. Thus, the ribbon assemblydisclosed in this publication does not have the capability of removingthe primary coatings on the optical glass fibers simultaneously withremoval of the matrix material during ribbon stripping, so as to provideresidue-free bare optical glass fibers.

Published European patent application 0527266 discloses a ribbon cablecontaining a lubricating “interfacial layer” which separates the matrixmaterial from the coated optical glass fibers. The interfacial layerfacilitates easy removal of the matrix material from the coated opticalglass fibers. While this publication discloses at page 3, line 15, thatthe buffer layer and first protective coating can be stripped in onestep, there is no disclosure teaching how to accomplish such anoperation. Furthermore, the lubricating interfacial layer will inhibitsimultaneous removal of the first protective coating with the matrixmaterial. Thus, this publication does not teach how to make a ribbonassembly having the capability of removing the primary coatings on theoptical glass fibers simultaneously with the matrix material duringribbon stripping, so as to provide residue-free bare optical glassfibers.

U.S. Pat. No. 4,900,126 discloses a ribbon cable in which the bondingadhesive forces between the ink layer and the primary coatings on theoptical glass fibers are greater than the bonding between the ink layerand the matrix material. In this manner, the matrix material can beeasily removed from the ink coated optical glass fibers without removingthe ink layer. However, this patent does not address the problemsassociated with removing the primary coating layers simultaneously withthe matrix material.

U.S. Pat. No. 4,660,927 teaches a silicone-coated optical fiber in whichthe soft silicone coating is easily peeled from the surface of theoptical glass fibers by finger pressure. The coating contains a firstsiloxane component having aliphatic unsaturated groups and a secondsiloxane component having mercaptoalkyl groups. Because such a coatingis easily peelable, as by rubbing with finger pressure, the coating hasinsufficient adhesion to the surface of the optical glass fibers toprevent delamination during most uses. Furthermore, this patent does notaddress the problems of ribbon stripping, but rather only the strippingof a single optical glass fiber. It is generally known that threecoating systems (inner primary coating, outer primary coating, and inkcoating) having acceptable single fiber strippability will exhibitdramatically different levels of strippability characteristics when usedin ribbon form.

U.S. Pat. No. 4,496,210 provides a radiation-curable optical fibercoating composition containing a polysiloxane. However, this patent doesnot address the problems associated with ribbon stripping.

Japanese Patent Application H3-35210 teaches to combine a liquidlubricant, such as liquid silicone oil or liquid aliphatic oil, with amercaptosilane compound in an inner primary coating composition. Duringstripping, when the bond between the surface of the optical glass fiberand inner primary coating is broken the liquid lubricant invades theboundary between the surface of the optical glass fiber and the innerprimary coating. The liquid lubricant must not have a high compatibilitywith the inner primary coating or it will not bleed out of the innerprimary coating during stripping. However, this document fails to teacha system to adjust the level of fiber friction between the adjacentsurfaces of the optical glass fiber and the inner primary coating to alevel which provides a resistive force that is less than the cohesivestrength of the inner primary coating. Thus, while this document teachesthat the inner primary coating can be stripped more easily byincorporating liquid lubricant compounds, the inner primary coating willstill leave unwanted residue on the surface of the optical glass fiberif the above described fiber friction forces are at a level whichprovide a resistive force that is greater than the cohesive strength ofthe inner primary coating.

One primary coating composition available from JSR Corporation,designated as R-1055, is specified as having, inter alia, a viscosity of5000 cps @ 25° C., a glass transition temperature of −4° C., a shrinkagevalue of 2.9%, a tensile strength value of 0.21 kg/mm², a tensileelongation value of 195%, an adhesion force of 20 g/cm and a Young'smodulus @ 23° C. of 0.12 kg/mm². When this composition was tested inaccordance with the test methods herein, it had a measured crackpropagation value of 1.56 mm (standard deviation 0.2), and a fiberpull-out friction value of 26.3 g/mm (standard deviation 1.65).

There are many test methods which may be used to determine theperformance of a ribbon assembly during ribbon stripping. An example ofa suitable test method for determining the stripping performance of aribbon is disclosed in the article by Mills, G., “Testing of 4- and8-fiber ribbon strippability”, 472 International Wire & Cable SymposiumProceedings (1992), the complete disclosure of which is incorporatedherein by reference.

Many attempts have been made to understand the problems associated withribbon stripping and to find a solution to increase ribbon strippingperformance. The following publications attempt to explain and solve theproblems associated with ribbon stripping: K. W. Jackson, et. al., “TheEffect of Fiber Ribbon Component Materials on Mechanical andEnvironmental Performance”, 28 International Wire & SymposiumProceedings (1993); H. C. Chandon, et. al., “Fiber Protective Design forEvolving Telecommunication Applications”, International Wire & SymposiumProceedings (1992); J. R. Toler, et. al., “Factors Affecting MechanicalStripping of Polymer Coatings From Optical Fibers”, International Wire &Cable Symposium Proceedings (1989); and W. Griffioen, “Strippability ofOptical Fibers”, EFOC & N, Eleventh Annual Conference, Hague (1993).

The ability of a ribbon assembly to ribbon strip cleanly so as toprovide bare optical glass fibers that are substantially free of residueis still unpredictable and the factors affecting ribbon stripping arenot fully understood. There is still a need for an understanding of howthe problems of ribbon stripping occur and a solution to these problems.

SUMMARY OF THE INVENTION

It is an objective of the present invention to provide a novel ribbonassembly having improved ribbon stripping capabilities. It is anotherobjective of the present invention to provide a novel ribbon assemblywhich after ribbon stripping provides bare optical glass fibers whichare substantially free of residue, that must be removed prior to formingconnections to the respective selected bare optical fibers.

Surprisingly, the above objects and other objects are and have beenobtained by the following. The present invention provides a novel ribbonassembly comprising:

a plurality of coated optical glass fibers, at least one optical glassfiber coated with at least an inner primary coating and an outer primarycoating, and optionally an ink coating; and

a matrix material bonding said plurality of coated optical glass fiberstogether, wherein said inner primary coating is adapted to provide thecombination of properties of:

(i) sufficient adhesion to said optical glass fiber to preventdelamination during handling and in the presence of moisture; and

(ii) a fiber friction force between said optical glass fiber and saidinner primary coating which has been so adjusted as to allow the innerprimary coating to slide readily off from the optical glass fiber whileleaving substantially no residue on the surface of said optical glassfiber during ribbon stripping, when a stripping force which is less thanthe cohesive strength of said inner primary coating is applied to saidribbon assembly.

Also provided is a novel ribbon assembly comprising:

a plurality of optical glass fibers, at least one coated optical glassfiber coated with at least an inner primary coating and an outer primarycoating, and optionally an ink coating; and

a matrix material bonding said coated optical glass fibers together,

and wherein said inner primary coating is adapted to provide a fiberpull-out friction of about 30 grams/millimeter or less at a rate ofabout 0.1 mm/sec in combination with a crack propagation characteristicof at least about 1 millimeter at a rate of 0.1 mm/sec.

The present invention further provides a coated optical glass fibercomprising:

an optical glass fiber;

an inner primary coating on the surface of said optical glass fiber;

an outer primary coating substantially co-extensive with the externalsurface of said inner primary coating, wherein said inner and outerprimary coatings are so formulated and selected so as to provide a ratioof (i) the change in length of the inner primary coating from an ambienttemperature to a ribbon stripping temperature to (ii) the change inlength of the outer primary coating from said ambient temperature tosaid ribbon stripping temperature of less than about 1.5:1; and

optionally an ink coating adjacent to said outer primary coating.

The invention further relates to a ribbon assembly containing at leastone of these coated optical glass fibers.

The present invention further relates to a novel radiation-curableoligomer which can be used to adjust the fiber friction to a level suchthat the resulting adhesive resistive force level is less than thecohesive strength of the inner primary coating. The novelradiation-curable oligomer comprises:

at least one glass coupling moiety;

at least one slip agent moiety; and at least one radiation-curablemoiety, wherein said glass coupling, glass adhesion, and radiationcurable moieties are each covalently linked to said oligomer.

Also provided is a radiation-curable, inner primary coating compositioncontaining the composite oligomer, a coated optical glass fiber madefrom the coating composition, and a ribbon assembly containing at leastone such coated optical glass fiber.

The present invention also provides a radiation-curable, inner primarycoating composition comprising at least one radiation-curable oligomeror monomer and a wax. Preferably, the wax is present in an amountsufficient to provide a fiber friction between an inner primary coatingformed from said coating and an optical glass fiber such that there isexhibited a resistive force that is less than the cohesive strength ofsaid coating formed from said composition. The invention also provides acoated optical glass fiber having an inner primary coating whichcontains a wax, and a ribbon assembly which contains at least one suchcoated optical glass fiber.

The present invention further provides a coated optical glass fiberhaving an inner primary coating which has been formulated from aradiation-curable, inner primary coating composition containing aradiation-curable silicone oligomer or a silicone compound. Preferably,the radiation-curable silicone oligomer or silicone compound is presentin an amount sufficient to provide a fiber friction between the innerprimary coating and the optical glass fiber such that there is exhibiteda resistive force which is less than the cohesive strength of the innerprimary coating. The invention also provides a ribbon assembly whichcontains at least one such coated optical glass fiber.

The present invention also provides a coated optical glass fiber havingan inner primary coating which has been formulated from aradiation-curable, inner primary coating composition containing aradiation-curable fluorinated oligomer or a fluorinated compound.Preferably, the radiation-curable fluorinated oligomer or fluorinatedcompound is present in an amount sufficient to provide a fiber frictionbetween the inner primary coating and the optical glass fiber such thatthere is exhibited a resistive force that is less than the cohesivestrength of the inner primary coating. The invention further provides aribbon assembly which contains at least one such coated optical glassfiber.

The present invention also provides a radiation-curable, inner primarycoating composition comprising at least one radiation-curable oligomeror monomer and a solid lubricant which is substantially insoluble in thecomposition. Preferably, the solid lubricant is present in an amountsufficient to provide a fiber friction between an inner primary coatingformed from said coating and an optical glass fiber such that there isexhibited a resistive force which is less than the cohesive strength ofsaid coating formed from said composition. The invention also provides acoated optical glass fiber having an inner primary coating whichcontains a solid lubricant, and a ribbon assembly which contains atleast one such coated optical glass fiber.

The present invention further provides a ribbon assembly comprising aplurality of coated optical glass fibers, at least one optical glassfiber coated with at least an inner primary coating and an outer primarycoating, and optionally an ink coating, and a matrix material bondingsaid plurality of coated optical glass fibers together. The innerprimary coating is formulated from a radiation-curable inner primarycoating composition containing at least one radiation-curable urethaneoligomer comprising at least one polymeric block and at least onefunctional group capable of polymerization in the presence of actinicradiation connected to said at least one polymeric block. The coatingcomposition has a concentration of urethane groups which is selected toprovide said inner primary coating with a fiber friction force levelbetween said optical glass fiber and said inner primary coating incombination with a crack propagation level that provides the innerprimary coating with the functional capability of sliding off of theoptical glass fiber and leaving substantially no residue on the surfaceof said optical glass fiber during ribbon stripping when a strippingforce which is less than the cohesive strength of said inner primarycoating is applied to said ribbon assembly.

The present invention further provides a ribbon assembly comprising aplurality of coated optical glass fibers, at least one optical glassfiber coated with at least an inner primary coating and an outer primarycoating, and optionally an ink coating, and a matrix material bondingsaid plurality of coated optical glass fibers together. The innerprimary coating is formulated from a radiation-curable inner primarycoating composition containing at least one radiation-curable oligomercomprising at least one polymeric block and at least one functionalgroup capable of polymerization in the presence of actinic radiationconnected to said at least one polymeric block. The polymeric block hasa molecular weight which is selected to provide said inner primarycoating with a fiber friction force level between said optical glassfiber and said inner primary coating in combination with a crackpropagation level that provides the inner primary coating with thefunctional capability of sliding off of the optical glass fiber andleaving substantially no residue on the surface of said optical glassfiber during ribbon stripping when a stripping force which is less thanthe cohesive strength of said inner primary coating is applied to saidribbon assembly.

The invention also provides a radiation-curable, inner primary coatingcomposition formulated from a composition comprising at least oneurethane oligomer having at least one polymeric block and at least onefunctional group capable of polymerization in the presence of actinicradiation connected to said at least one polymeric block. The coatingcomposition has a concentration of urethane groups that is so selectedto provide said inner primary coating with a fiber friction force levelbetween an optical glass fiber and an inner primary coating formed fromsaid coating composition in combination with a crack propagation levelwhich provides the inner primary coating with the functional capabilityof sliding off the optical glass fiber and leaving substantially noresidue on the surface of said optical glass fiber during ribbonstripping when a stripping force which is less than the cohesivestrength of said inner primary coating is applied to said inner primarycoating.

The present invention further provides a radiation-curable, innerprimary optical glass fiber coating composition formulated from acomposition comprising at least one radiation-curable oligomer having atleast one polymeric block and at least one functional group capable ofpolymerization in the presence of actinic radiation connected to said atleast one polymeric block. The polymeric block has a molecular weight soselected to provide said inner primary coating with a fiber frictionforce level between said optical glass fiber and said inner primarycoating in combination with a crack propagation level that provides theinner primary coating with the functional capability of sliding off theoptical glass fiber and leaving substantially no residue on the surfaceof said optical glass fiber during ribbon stripping when a strippingforce which is less than the cohesive strength of said inner primarycoating is applied to said inner primary coating.

The present invention also provides coated optical glass fiberscontaining at least one inner primary coating formed from the aboveradiation-curable, inner primary coating compositions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a longitudinal cross-sectional view of a coatedoptical glass fiber.

FIG. 2 illustrates a representative graph of the normalized strip forcerequired to slide an optical fiber ribbon coating composite along thesurface of an optical glass fiber.

FIG. 3 illustrates the ratchet effect of an inner primary coatingsliding off an optical glass fiber during ribbon stripping.

FIG. 4 is a graph of the change in length L (“dL”) for a commerciallyavailable outer primary coating as the temperature is increased.

FIG. 5 illustrates a partial cross-sectional view of a coated opticalglass fiber.

FIG. 6 illustrates a hypothetical contour plot for determining thepredicted strip cleanliness.

FIG. 7 illustrates a graph of the fiber pull-out friction versusurethane concentration.

FIG. 8 illustrates a graph of the fiber pull-out friction versusurethane concentration.

FIG. 9 illustrates a graph of the fiber pull-out friction versusurethane concentration.

FIG. 10 illustrates a graph of the fiber pull-out friction versusurethane concentration.

FIG. 11 illustrates a graph of the fiber pull-out friction versusurethane concentration.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The invention will now be explained in detail with reference to theattached drawings.

Based on extensive experimentation, it is now believed that ribbonstripping functionally involves two phases, a first adhesion breakingphase and a second frictive sliding phase. This can be characterized bythe following equation (1):

F _(stripping) =F _(adhesive) +F _(friction)  (1)

where

F_(stripping) is the stripping force applied to the inner primarycoating;

F_(adhesive) is the force required to break the adhesive forces betweenthe optical glass fiber and the inner primary coating; and

F_(friction) is a function of the normal force the inner primary coatingexerts against the surface of the optical glass fiber and thecoefficient of friction of the inner primary coating.

F_(friction) is equal to F_(static), defined as the condition when theinner primary coating is in a static position, and F_(friction) is equalto F_(kinetic) defined as when the inner primary coating is in motionrelative to the optical glass fiber.

During the adhesion breaking phase, the adhesive force between the innerprimary coating and the surface of the optical glass fiber must bebroken to delaminate the inner primary coating from the surface of theoptical glass fiber. Once that adhesive force is broken, and the innerprimary coating is delaminated from the surface of the optical glassfiber, the fiber friction force between the inner primary coating andthe surface of the optical glass fiber must then be overcome to removethe inner and outer primary coatings, along with the matrix material,from the optical glass fiber.

The adhesive force between the inner primary coating and the surface ofthe optical glass fiber is generally increased by an increase in thefollowing:

(1) covalent bonding, for example from glass adhesion promoters;

(2) weak molecular interactions, such as Van der Waal's attractions,hydrogen-bonding, electrostatic, and the like;

(3) static coefficient of friction;

(4) surface energy of the inner primary coating and surface energy ofthe optical glass fiber;

(5) surface roughness; and

(6) adhesive bonding area.

The adhesive force between the inner primary coating and the surface ofthe optical glass fiber is generally decreased by an increase in thetemperature.

The fiber friction force between the inner primary coating and thesurface of the optical glass is generally increased by an increase inone or more of the following:

(1) the normal force of the inner primary coating against the surface ofthe optical glass fiber at the ribbon stripping temperature;

(2) the static and kinetic coefficient of friction at the ribbonstripping temperature;

(3) surface roughness; and

(4) frictive area.

The normal force includes weak molecular interactions, such as Van derWaal's attractions, hydrogen-bonding, electrostatic, and the like,between the surface of the optical glass fiber and the inner primarycoating. In general, the fiber friction force is decreased with anincrease in temperature.

The rigidity and integrity of the outer primary coating at the ribbonstripping temperature can also affect the frictive force. During ribbonstripping the outer primary coating, ink coating, and other rigidcoating layers, such as the matrix material, provide the stiffeningbackbone which allows for intact removal of the matrix material andinner and outer primary coatings to provide a cohesive tube (hereinafterreferred to as “coating tube”). If the rigidity and integrity areinsufficient, the outer primary coating can buckle during ribbonstripping, which can significantly increase the fiber friction forceand/or induce shearing stresses causing integrity failure of the innerprimary coating resulting in undesirable residue on the surface of theoptical glass fiber.

Preferably, the adhesion between the matrix material and the ink coatingor colored outer primary coating is greater than the adhesion betweenthe inner primary coating and the surface of the optical glass fiber toensure that the inner primary coating delaminates from the surface ofthe optical glass fiber during ribbon stripping. Similarly, both theadhesion between the ink coating and the outer primary coating, and theadhesion between outer primary coating and the inner primary coating,should be greater than the adhesion between the inner primary coatingand the surface of the optical glass fiber to ensure that the innerprimary coating delaminates from the surface of the optical glass fiber,as well as to provide a cohesive coating tube during ribbon stripping.Usually, the adhesion between the matrix material and the colored outerprimary coating or ink coating, as well as the adhesion between each ofthe coating layers is sufficient to ensure delamination of the innerprimary coating from the surface of the optical glass fiber duringribbon stripping because the matrix material and coating layers mainlycomprise organic materials. In general, layers of materials havingsimilar properties, such as an adjacent organic layer/organic layerbond, tend to bond more easily together than layers having dissimilarproperties, such as an organic layer/inorganic layer bond.

FIG. 1 illustrates an optical glass fiber 7 coated with an inner primarycoating 8 and a commercially available outer primary coating 9. Thelength of the inner primary coating in FIG. 1 shown at 20 has beenselected to be 35 mm because this is a typical length of the coatingsstripped from the ends of the optical glass fibers during ribbonstripping. When a typical ribbon stripping tool is applied to a ribbonassembly, pressure is applied to the ribbon assembly between heatedplates. At the ends of the plates near the cut made in the matrixmaterial and inner and outer primary coatings, the inner primary coatingcan form an initial delamination site on the optical glass fiber, shownat 27 and 28 (referred to as debond area). Because the areas 27 and 28of the inner primary coating are delaminated, they must be subtractedfrom that area of the inner primary coating which is still bonded to thesurface of the optical glass fiber when measuring the adhesive bondingarea between the inner primary coating and the surface of the opticalglass-fiber. The radius of the optical glass fiber is 62.5 microns,shown at 22. The radius of the outer surface of inner primary coating is95 microns, shown at 24. The radius of the outer surface of the outerprimary coating is 125 microns, shown at 26. From FIG. 1, the adhesivebonding area is equal to the glass surface area (13.744 mm²) minus thedebond area. The frictive area is the total glass surface area of thesection to be stripped during ribbon stripping (13.744 mm²).

It is believed that during ribbon stripping the inner primary coatingmay ratchet off the optical glass fiber, as shown in FIG. 2. FIG. 2 is ademonstration of the adhesive force and fiber friction force beingovercome by the stripping force applied to the inner primary coatingduring the ribbon stripping process. As stripping force is applied fromthe stripping tool to the inner primary coating, the stripping forceincreases to a level at which the adhesive force between the innerprimary coating and the surface of the optical glass fiber is overcome,which is shown at 1. At this level, the inner primary coating begins todelaminate from the surface of the optical glass fiber. Then, thestripping force decreases as the inner primary coating delaminates fromthe optical glass fiber, shown generally at 2. Once delamination hascompleted, shown at 3, the inner primary coating slides along thesurface of the optical glass fiber and the stripping force decreases tothe level shown at 4. As the inner primary coating is being slid off ofthe optical glass fiber the stripping force required to slide the innerprimary coating against the optical glass fiber ratchets between thehigher static fiber friction force and the lower kinetic fiber frictionforce.

The static fiber friction force is a function of the static coefficientof friction of the inner primary coating and the normal force of theinner primary coating against the optical glass fiber. The kinetic fiberfriction force is a function of the kinetic coefficient of friction ofthe inner primary coating and the normal force of the inner primarycoating against the optical glass fiber. The static fiber friction forceresists initial sliding movement and the kinetic fiber friction forceresists subsequent sliding movement. In other words, once the adhesivebond is broken and the static fiber friction force is overcome, shown at3, the inner primary coating slides a set distance until the kineticfiber friction force prevents further motion and the inner primarycoating becomes momentarily stuck in place against the surface of theoptical glass fiber, shown at 4. As the stripping force increases, andbefore the inner primary coating resumes its motion relative to theoptical glass fiber, the potential energy is stored in the inner primarycoating which produces a tensile force and a stripping force within theinner primary coating. The tensile force is opposed to the normal forceand the stripping force is opposed to the fiber friction force.

The motion force (“F_(motion)”) of the inner primary coating is a vectorsum of the tensile force (“F_(tensile)”) and the stripping force(“F_(stripping)”). The resistive force (“F_(resistive)”) is a vector sumof the fiber friction force (“F_(friction)”) and the normal force(“F_(normal)”) on the inner primary coating against the surface of theoptical glass fiber.

Once the motion force (“F_(motion)”) exceeds the resistive force(“F_(resistive)”) the inner primary coating begins to slide, shown at 5.The inner primary coating quickly slides a set distance and then becomesmomentarily stuck, shown at 6. The distance the inner primary coatingslides along the surface of the optical glass fiber between the points 5and 6 in FIG. 2 is referred to as slip-stick distance. The slip-stickdistance will vary and be dependent upon the materials used in the innerprimary coating and optical glass fiber, and will also be dependent uponrandom probability due to non-homogeneity in the inner primary coatingand optical glass fiber surface.

FIG. 3 further explains the ratcheting effect during ribbon stripping byway of example. As shown in FIG. 3, a partial longitudinal cross-sectionof an optical glass fiber is shown at 7. A two-dimensional vectorexplanation will be used herein for ease of explanation. However, it isunderstood that a coated optical glass fiber is a three-dimensionalobject and all of the described vectors need to be extended anadditional dimension.

The optical glass fiber is coated with an inner primary coating shown at8, and an outer primary coating shown at 9. The thickness “Y” of theinner primary coating is about 37.5 microns, shown at 12. As strippingforce is indirectly applied to the inner primary coating in thedirection shown at 10, the inner primary coating is deformed a pre-slipdistance “X”, shown at 11, at which point the inner primary coatingdelaminates and begins to ratchet along the surface of the optical glassfiber. The stripping force required to make the inner primary coatingbegin to ratchet along the surface of the optical glass fiber can becalculated as follows. The length of the tensile deformation of thedeformed inner primary coating at the level of strip force required tomake the inner primary coating begin to slide after being momentarilystuck to the surface of the optical glass fiber “Z” is shown at 13. The% elongation of the deformed inner primary coating can be calculatedfrom the values Z and Y using the following equation (2):

(Z−Y)/Y=% elongation  (2)

From a stress/strain curve, one skilled in the art can readily use the %elongation to calculate the tensile force (F_(tensile)) required toinitiate sliding of the inner primary coating from a static position.

The vector for the static fiber friction force F_(friction) is shown at19. When F_(motion) is greater than F_(resistive), the inner primarycoating will begin to slide from a static position. F_(motion), shown at15, is the vector sum of F_(tensile), shown at 14, and F_(stripping),shown at 16. F_(resistive) shown at 17, is the vector sum ofF_(friction) shown at 19, and F_(normal), shown at 18.

If either of the vector components F_(stripping) or F_(tensile) isgreater than the corresponding inner primary coating resistive vectorcomponents (shear strength and tensile strength, respectively), then theinner primary coating will cohesively fail during ribbon strippingleaving an undesirable residue of inner primary coating material on thesurface of the optical glass fiber.

Similarly, if either of the vector components F_(friction) or F_(normal)is greater than the inner primary coating resistive vector components(shear strength and tensile strength, respectively), then the innerprimary coating will cohesively fail during ribbon stripping leaving anundesirable residue of inner primary coating material on the surface ofthe optical glass fiber.

More generally, the inner primary coating will cohesively fail ifF_(resistive) is greater than the cohesive strength of the inner primarycoating. Thus, to prevent such residue, the F_(friction) and/orF_(normal) should be so adjusted as to provide a F_(resistive) that isless than the cohesive strength of the inner primary coating.

The term “cohesive strength” of the inner primary coating is used hereinto mean the amount of force necessary to destroy the integrity of theinner primary coating. Thus, a higher cohesive strength will require agreater amount of force to destroy the integrity of the inner primarycoating. The cohesive strength can be measured using any one of (1) theshear strength of the inner primary coating, (2) the tensile strength ofinner primary coating, or (3) the crack propagation of the inner primarycoating. Preferably, the cohesive strength is measured using the crackpropagation. test, as described herein below.

This residue can interfere with the optical glass fiber ribbon massfusion splicing operation, and therefore must be removed prior tosplicing by wiping. The step of removing the residue can cause abrasionsites on the bare optical glass fiber, thus compromising the strength ofthe connection.

Once the adhesive bonds have been broken and the inner primary coatinghas been delaminated from the surface of the optical glass fiber, theability of a ribbon assembly to strip cleanly during ribbon strippingand to provide bare optical glass fibers which are substantially free ofresidue can be understood using the following simplified equation (3):

F _(friction) =C _(f) ×F _(normal)  (3)

where F_(friction) is the static frictive force between the innerprimary coating and the optical glass fiber;

C_(f) is the static coefficient of friction of the inner primary coatingon the surface of the optical glass fiber, and

F_(normal) is the normal force of the inner primary coating against thesurface of the optical glass fiber.

Hereinafter, the use of the term “fiber friction” in the specificationand claims refers to the static fiber friction force.

In general, the lower the fiber friction, the lower the resistive force,and the easier the inner primary coating can be removed from the surfaceof the optical glass fiber without leaving a residue. From equation 3,it is evident that the fiber friction can be reduced by decreasingeither or both the static coefficient of friction or the normal force.

Each inner primary coating has a specific cohesive strength whichmaintains the integrity of the inner primary coating. The greater thecohesive strength of the inner primary coating the greater the amount ofenergy required to break apart or fracture the inner primary coating.Thus, an inner primary coating having a higher cohesive strength canwithstand greater stripping forces during ribbon stripping, withoutbreaking apart and leaving residue on the surface of the optical glassfiber, than an inner primary coating having a lower cohesive strength.

From the above discussion, it is clear that if the fiber friction is ata level which provides a resistive force that is greater than thecohesive strength of the inner primary coating, then the inner primarycoating will break apart leaving residue on the surface of the opticalglass fiber. Thus, when selecting or formulating the inner and outerprimary coatings, the fiber friction level should be adjusted takinginto account the cohesive strength of the inner primary coating so thatfiber friction provides resistive force that is less than the cohesivestrength of the inner primary coating.

Minimizing the Normal Force

From the above equations, the fiber friction force between the opticalglass fiber and inner primary coating can be lowered by reducing thenormal force of the inner primary coating against the surface of theoptical glass fiber. In general, the greater the normal force, thegreater the fiber friction force between the optical glass fiber and theinner primary coating. In other words, the harder the inner primarycoating is pressing against the surface of the optical glass fiber, theharder it will be to slide the inner primary coating against the surfaceof the optical glass fiber and the greater the chances of leavingresidue from the inner primary coating on the surface of the opticalglass fiber. Since the normal force is a component of the fiberfriction, lowering the normal force will lower the fiber friction. Thenormal force should therefore be adjusted or selected so as to provide anormal force vector component and a fiber friction vector component thatprovides a vector sum (resistive force) which is less than the cohesivestrength of the inner primary coating.

During ribbon stripping, the inner primary and outer primary coatingsare heated, typically to about 90 C. to about 120 C. Because innerprimary coatings usually have a lower Tg than that of outer primarycoatings, inner primary coatings usually expand to a greater extent thanthe outer primary coatings during ribbon stripping. Thus, when the innerand outer primary coatings are heated, the inner primary coating expandsto a greater extent than the outer primary coating causing a pressurebuild-up within the inner primary coating and between the surface of theoptical glass fiber and the outer primary coating. This pressure buildupin the inner primary coating increases the normal force of the innerprimary coating against the optical glass fiber, thereby increasing thefiber friction force between the inner primary coating and the surfaceof the optical glass fiber. Thus, the resistive force will be increasedby an increase in the normal force vector component and an increase inthe fiber friction vector component.

It is believed that the inner primary coating expands to a greaterextent than the outer primary coating during ribbon stripping, at leastin part due to the following reason. At temperatures below the Tg of thepolymeric coating, the polymers present in the coating tend to act“glass-like”, and therefore have a low coefficient of expansion.However, at temperatures above the Tg of the polymeric coating, thepolymers tend to act “rubber-like” and therefore have a highercoefficient of expansion than when below the Tg of the polymericcoating. As the temperature of the ribbon assembly is raised duringribbon stripping the polymer present in the inner primary coating willusually be at a temperature above their Tg and be more “rubber-like”well before the polymers present in the outer primary coating reachtheir Tg. Thus, as the applied stripping temperature is raised, the“rubber-like” polymer present in the inner primary coating will expandto a much greater extent, than the “glass-like” polymer in the outerprimary coating.

The Tg of the inner primary coating and that of the outer primarycoating usually cannot be matched because the outer primary coatingshould have a higher Tg to provide the tough protective propertiesrequired of the outer primary coating. In general, the Tg of the outerprimary coating is above 60° C., whereas the Tg of the inner primarycoating is usually below 10° C., preferably below about 0° C., morepreferably below about −10° C., and most preferably below about −20° C.

However, it has been found that the relative expansion characteristicsof the inner and outer primary coatings can be adjusted withoutsubstantially affecting the Tg of the coatings. The expansioncharacteristics of the desired inner and outer primary coatings shouldfirst be measured as follows. The change in expansion from the ambientworking temperature of the ribbon assembly to the ribbon strippingtemperature measured in one plane “dL” is divided by an initial lengthof the one plane measured at the ambient working temperature Qf theribbon assemble “L”, hereinafter referred to as “(dL/L)”. Ambientworking temperatures of ribbon assemblies are usually about 0° C. toabout 30° C. It will be appreciated that for most coating compositionsthe design ribbon stripping temperatures are usually about 90° C. toabout 120° C., but may be different depending on the specific designparameters for the particular coating composition.

The inner and/or outer primary coatings should be selected orreformulated so as to maximize the (dL/L) of the outer primary coatingand while minimizing the (dL/L) of the inner primary coating. Ideally,the (dL/L) of the outer primary coating should be greater than that ofthe inner primary coating whereby the outer primary coating willtheoretically exert a normal force on the inner primary coating in adirection away from the optical glass fiber during ribbon stripping.However, such high (dL/L) values for the outer primary coating incombination with retention of the desired toughness properties of theouter primary coating are usually unattainable. Nevertheless, increasingthe (dL/L) of the outer primary coating can significantly reduce theincrease in normal force on the inner primary coating during ribbonstripping to provide a clean optical glass fiber which is substantiallyfree of residue.

FIG. 4 is a graph of the change in L (“dL”) for a commercially availableouter primary coating as the temperature is increased. In particular,for an L of 23.2 mm, the dL for a temperature change from 25 C. (exampleof ambient temperature) to 100 C. (example of ribbon strippingtemperature) can be calculated as follows: $\begin{matrix}{{d\quad {L/L}} = {\left( {{delta}\quad L} \right)/L}} \\{= {(0.4)/23.2}} \\{= {.01724}}\end{matrix}$

The dL/L value is independent of the length of the coating selected forthe measurement. Thus, for different L values, the dL/L will beconstant.

The normal force on the inner primary coating against the optical glassfiber, which is caused by the differential in expansion between theinner primary coating and outer primary coating during ribbon stripping,can be calculated as follows. FIG. 5 illustrates a cross-sectional viewof a glass optical fiber 7, coated with an inner primary coating 8 andan outer primary coating 9. The outer primary coating 9 is the same asthat in FIGS. 1 and 4. The radius of the outer surface of the innerprimary coating at 25 C. is 95 microns, shown at 40. The radius of theinner surface of the outer primary coating at 25 C. is 95 microns, alsoshown at 40. As the temperature of the ribbon assembly is increased to100 C. during ribbon stripping, the inner primary coating and outerprimary coating expand.

The radius of the inner surface of the outer primary coating at 100 C.is 96.379 microns, shown at 42. This value was calculated as follows.The (dL/L) for the outer primary coating material heated from 25 C. to100 C. is 0.01724, as calculated from FIG. 4. The radius of the innersurface of the outer primary coating at 25 C. (95 microns) is multipliedby (1+dL/L) for a temperature change of 25 C. to 100 C. (1.01724) whichprovides a radius of the inner surface of the outer primary coating at100 C. of 96.638 microns. However, this value must be corrected to takeinto account the expansion in the thickness of the outer primarycoating. The outer primary coating has as thickness of 30 microns at 25C. To obtain the thickness at 100 C., the thickness at 25 C. (30microns) is multiplied by (1+dL/L) for a temperature change of 25 C. to100 C. (1.01724), which provides a thickness of 30.5172 microns. Thus,the thickness of the outer primary coating expands 0.5172 microns whenheated from 25 C. to 100 C. One half of this expansion occurs in thedirection of the inner primary coating. This assumes that the innerprimary coating will not substantially resist the expansion of the outerprimary. Thus, one half of 0.5172 must be subtracted from the valueobtained above for the radius of inner surface of the outer primarycoating at 100 C. (96.638 microns) to obtain a corrected value of 96.379microns. The change in radius over the temperature change from 25 C. to100 C. “dR” divided by the radius at 25 C. “R” is then calculated toprovide the value (dR/R).

The above measurements can be performed on the inner primary coatingselected to provide a value (dR/R) for the inner primary coating. Theradius of the inner primary coating at 100 C. is shown at 44. The normalforce on the inner primary coating against the optical glass fiber,which is caused by the differential in expansion between the innerprimary coating and outer primary coating during ribbon stripping isshown at 46.

The % expansion of the inner primary coating can be calculated from thefollowing:

((dR/R)_(inner primary)−(dR/R)_(outer primary))×100%

From a stress/strain curve, one skilled in the art can easily use the %expansion to calculate the pressure of the inner primary coating againstthe optical glass fiber, which is caused by the differential inexpansion between the inner and outer primary coating during ribbonstripping. Multiplying the pressure by the surface area of the innerprimary coating against the optical glass fiber provides the normalforce of the inner primary coating against the surface of the opticalglass fiber.

Preferably, the (dR/R)_(inner primary) is decreased and/or the(dR/R)_(outer primary) is increased to reduce the differential inexpansion between the inner and outer primary coating during ribbonstripping, thereby reducing the normal force of the inner primarycoating against the surface of the optical glass fiber.

Based on the above, it has been found that the normal force can bedecreased by reducing the pressure increase of the inner primary coatingduring ribbon stripping, by reformulating the inner primary coatingand/or outer primary coating to provide one or more of the followingproperties:

(1) decreasing the elastic modulus (at ribbon stripping temperature) ofthe outer primary coating so that it can stretch to a greater extent torelieve more of the pressure build-up of the inner primary coatingduring ribbon stripping,

(2) increasing the (dL/L) of the outer primary coating so that the outerprimary coating expands to a greater extent to allow for more expansionof the inner primary coating during ribbon stripping, and/or

(3) decreasing the (dL/L) of the inner primary coating to reduce thepressure build-up of the inner primary coating.

The elastic modulus (at ribbon stripping temperature) of the outerprimary coating can be decreased by reducing the crosslink density ofthe outer primary coating. The elastic modulus is determined by theElastic Modulus Test method, as discussed in the DESCRIPTION OF TESTMETHODS, below. Preferably, the elastic modulus of the outer primarycoating is adjusted to be between about 10 to about 40 MPa, morepreferably between about 10 to about 20 MPa, at the ribbon strippingtemperature. Outer primary coatings having an elastic modulus in therange of between about 15 to about 40 MPa, more preferably between about30 and 40 MPa, have also been found suitable as well as outer primarycoatings having an elastic modulus of greater than about 25 MPa. Whileit has been found that the crosslink density of the outer primarycoating can usually be reduced without causing undesirable effects, theTg of the outer primary coating should remain high, to provide the outerprimary coating with the necessary toughness related properties toprotect the optical glass fiber. For example, to reduce the crosslinkdensity of the outer primary coating without reducing the Tg tounacceptably low values, monofunctional monomers or oligomers, whichwhen cured exhibit a high Tg, can be used. Monofunctional is understoodherein as including monomers and oligomers having an average of about 1functional group capable of polymerization upon exposure to actinicradiation. A high Tg is herein understood to be at least about 40 C.,preferably at least about 50 C.

Examples of suitable high Tg producing monofunctional monomers andoligomers include, for example, isobornyl acrylate and vinylcaprolactam.Such monomers can be utilized in amounts of about 1% to about 80%,preferably about 10 to about 50% by weight of the total composition.

Very high Tg producing multifunctional monomers or oligomers, such astris-hydroxyethylisocyanurate triacrylate can also be used in amounts upto about 30%, preferably up to about 20% by weight, because they areeffective at greatly increasing the Tg of the outer primary coatingwithout excessively increasing the crosslink density.

The (dL/L) of the outer primary coating can be significantly increasedby incorporating a monomer or oligomer which when cured exhibits a high(dL/L). For example, a suitable (dL/L), at the desired ribbon strippingtemperature, for the outer primary coating has been found to be at leastabout 0.017, preferably at least about 0.02, and most preferably atleast about 0.023. These amounts can be expressed as percentageincreases in the length by multiplying by 100. Therefore, the outerprimary coating preferably increases in length over the change intemperature from ambient temperature to ribbon stripping temperature(“dL/L”) of at least about 1.7%, more preferably at least about 2%, andmost preferably at least about 2.3%. If the coefficient of friction ofthe inner primary coating and/or the dL/L of the inner primary coatingare sufficiently low enough, the dL/L of the outer primary coating canbe less than 1.7% and still provide a fiber friction and normal forcethat will result in a resistive force that is less than the cohesivestrength of the inner primary coating.

The high (dL/L) producing monomer or oligomer should be added in anamount sufficient to provide a cured outer primary coating with thedesired level of (dL/L). For example, the high (dL/L) monomer oroligomer can be added in an amount of about 10 to about 70% by weight,more preferably about 10 to about 50% by weight.

Examples of suitable high (dL/L) monomers or oligomers include isobornylacrylate, vinylcaprolactam, tricyclodecane dimethanol diacrylate, andthe adduct of 2 moles of hydroxyethylacrylate and 1 mole of isophoronediisocyanate.

The (dL/L) of the inner primary coating can be decreased by increasingthe crosslink density of the inner primary coating. However, whenreformulating the inner primary coating to increase the crosslinkdensity, the Tg of the inner primary coating should remain low toprovide the optical glass fiber with adequate protection frommicrobending. It has been found that the crosslink density can beincreased by using multifunctional monomers and oligomers. Examples ofsuitable multifunctional monomers and-oligomers include,hexanedioldiacrylate, trimethyolpropane triacrylate, andtripropyleneglycol diacrylate.

The ratio of the dL/L (inner primary) to the dL/L (outer primary) at thedesired ribbon stripping temperature should be low enough to provide afiber friction and normal force that results in a resistive forcebetween the inner primary coating and the optical glass fiber that isless than the cohesive strength of the inner primary coating. Ingeneral, the lower the ratio of dL/L (inner primary) to dL/L (outerprimary) the less the normal force that will be applied to the innerprimary coating against the surface of the optical glass fiber. Thus,the ratio of the dL/L (inner primary) to dL/L (outer primary) requiredto provide a fiber friction force that results in a resistive forcelower than the cohesive strength of the inner primary coating willdepend upon the coefficient of friction of the inner primary coating.The lower the coefficient of friction of the inner primary coating, thegreater the ratio of dL/L (inner primary) to dL/L (outer primary) thatcan be tolerated and still provide a fiber friction and normal forcewhich results in a resistive force that is less than the cohesivestrength of the inner primary coating.

It has been found that a suitable ratio for the dL/L (inner primary) tothe dL/L (outer primary) at the desired ribbon stripping temperature isless than about 2, preferably less than about 1.7, and most preferablyless than about 1.5.

The outer primary coating can also exert a force on the inner primary,which is caused by shrinkage of the outer primary coating duringradiation curing of the outer primary coating. Thus, to reduce thisforce oligomers and monomers can be selected to provide aradiation-curable composition that exhibits reduced shrinkage duringradiation-curing.

If an ink coating is present, the ink coating can also exert a normalforce on the inner primary coating in a manner similar to the normalforce exerted by the outer primary coating. However, the force exertedby the ink coating will generally be significantly less than the forceexerted by the outer primary coating because the ink coating isgenerally about an order of magnitude thinner than the outer primarycoating. The thickness of the ink layer is usually only about 3 to about8 microns.

If desired, the normal force exerted by the ink coating can be adjustedin a similar manner as adjusting the normal force exerted by the outerprimary coating, because the ink coating in general is also formed frommonomers and oligomers similar to those used to form the outer primarycoating. In particular, the (dL/L) of the ink coating can be adjusted tobe closer to the (dL/L) of the inner primary coating by reformulatingthe ink coating to utilize monomers and/or oligomers that result in acoating having a (dL/L) closer to the (dL/L) of the inner primarycoating, as described herein above in reference to the outer primarycoating.

The invention will be further explained by the following non-limitingexample.

COMPARATIVE EXAMPLES A-1 to A-2

The compositions shown in Table 1 represent commercially availablecoating compositions. Comparative Example A-1 is an example of an outerprimary coating and Comparative Example A-2 is an example of an innerprimary coating.

TABLE 1 Comp. Comp. Example Example A-1 A-2 Component (Amount in % byweight of total composition) Oligomer H-(T-PTMG650)₁ ₁₄-T-H 39 OligomerH-(I-PTGL2000)₂-I-H 51.41 Bisphenol A Diglycidylether 29 DiacrylateIsobornyl Acrylate 10 6.86 Hexanediol Diacrylate 8.5 PhenoxyethylAcrylate 10 Lauryl Acrylate 5.95 Ethoxylated Nonylphenol Acrylate 20.91Tripropyleneglycol Diacrylate 5.81 Vinyl Caprolactam 6.11 Diethylamine.1 Gamma Mercaptopropyl Trimethoxy 1 Silane Thiodiethylenebis(3,5-di-tert- .5 .31 butyl-4-hydroxy) hydrocinnamate2,4,6-Trimethylbenzoyl diphenyl 2 1.54 phosphine oxide1-Hydroxycyclohexylphenyl Ketone 1 The oligomers were formed by reactingthe following components: H = Hydroxyethyl Acrylate T = TolueneDiisocyanate I = Isophorone Diisocyanate PTGL2000 = 2000 molecularweight polymethyltetrahydrofurfuryl/polytetrahydrofurfuryl copolymerdiol (Mitsui, NY) PTMG650 = 650 molecular weightpolytetramethyleneglycol diol (Dupont)

The compositions were suitably cured by exposure to UV light from aFusion D lamp. The dL/L for each coating was measured over thetemperature range of 25 C., (ambient temperature) to 125 C. (highestusual stripping temperature).

For Comparative Example A-1, the dL/L for a temperature change fromambient temperatures (25 C.) to ribbon stripping temperatures (100 C.)was 1.42%.

For Comparative Example A-2, the dL/L for a temperature change fromambient temperatures (25 C.) to ribbon stripping temperatures (100 C.)was 2.3%.

Thus, the ratio of the dL/L (inner primary) to dL/L (outer primary) wasabout 1.6, which would be acceptable if the coefficient of friction ofthe inner primary coating was low enough. However, the inner primarycoating exhibited too high of a coefficient of friction, because thefiber friction estimated by using the fiber pull-out friction methoddescribed herein below was too great. The fiber pull-out friction was 39g/mm, which resulted in a resistive force that was greater than thecohesive strength of the inner primary coating. Therefore, substantialamounts of inner primary coating residue were left on the optical glassfiber after ribbon stripping using the above inner and outer primarycoatings.

Coefficient of Friction of Inner Primary Coating

From the above equations, fiber friction between the optical glass fiberand inner primary coating can also be adjusted by reducing thecoefficient of friction of the inner primary coating against the surfaceof the optical glass fiber. By reducing the coefficient of friction ofthe inner primary coating, the “rubber-like” drag of the inner primarycoating on the optical glass fiber is reduced.

Preferably, the coefficient of friction of the inner primary coating isreduced without reducing the adhesion of the inner primary coating tothe surface of the optical glass fiber. If the adhesion is reduced, thenundesirable delamination of inner primary coating from the surface ofthe optical glass fiber can occur.

It has been found that the fiber friction can be adequately adjusted toa value which provides resistive force below the cohesive strength ofthe inner primary coating by adjusting the coefficient of friction ofthe inner primary coating with the use of one or more of the novel slipadditives described herein. Surprisingly, the coefficient of frictioncan be reduced to such a level without substantially reducing theadhesion of the inner primary coating to the optical glass fiber asfollows.

Preferably, the ratio of the dL/L (inner primary) to the dL/L (outerprimary) is adjusted in combination with adjusting the coefficient offriction of the inner primary coating to provide a fiber friction valuewhich results in a resistive force that is less than the cohesivestrength of the inner primary coating.

In practice, ribbon assemblies are generally stripped using a heatedstripping tool. However, using the inventive concepts described herein,the present invention includes ribbon assemblies which surprisingly canbe ribbon stripped at much lower temperatures, such as ambienttemperatures, to provide bare optical glass fibers which aresubstantially free-of residue. It has been found that if the fiberfriction between the inner primary coating and the surface of theoptical glass fiber and/or the normal force is adjusted to a level whichprovides a resistive force lower than the cohesive strength of innerprimary coating, the ribbon assembly will be ribbon strippable.Therefore, if a ribbon assembly which is adapted to provide ribbonstrippability at ambient temperatures is desired, the fiber friction canbe adjusted to a level to provide a resistive force that is less thanthe cohesive strength of the inner primary coating using slip agents asdiscussed herein. Alternatively, if the ribbon assembly is adapted toprovide ribbon strippability at temperatures greater than ambienttemperatures, the resistive force can be adjusted to a level lower thanthe cohesive strength of the inner primary coating by adjusting theratio of the dL/L (inner primary) to the dL/L (outer primary) to providea lower normal force and fiber friction, and/or adjusting thecoefficient of friction of the inner primary coating using slip agentsto provide a lower fiber friction.

Novel Radiation-curable, Silicone-silane Oligomer

This invention also provides a novel type of radiation-curable oligomerthat can be used to adjust the fiber friction between the inner primarycoating and the surface of the optical glass fiber. Theradiation-curable oligomer comprises a glass coupling moiety, a slipagent moiety, and a radiation curable moiety, each moiety being linkedto a single composite oligomer molecule through covalent bonding toprovide a composite oligomer. Such linkage of all three moieties isheretofore unknown. Linkage of these moieties can be direct so that nointermediate linking group between the oligomer and the moiety isrequired. Alternatively, however, the linkage can be indirect by usingintermediate linking groups.

A variety of glass coupling, slip agent, and radiation curable moietiesare known in the art. The present invention can be practiced with use ofvarious embodiments using different combinations of these moieties toproduce a composite oligomer. A person skilled in the art will easily beable to prepare combinations of these various moieties from the presentdisclosure and general knowledge in the art.

Radiation-curing can occur by reaction of the composite oligomer'sradiation-curable moieties with themselves or with radiation-curablemoieties bound to other components of a formulation. In general, curingof the composite oligomer occurs in concert with other radiation-curablecomponents. Radiation-curing, in the present invention, is associatedwith reaction of the radiation-curable moiety, not with the glasscoupling or slip agent moieties. For example, although the glasscoupling moiety will be reactive, and is often sensitive to hydrolysisand condensation reactions, these types of reactions are not theprincipal cure mechanism.

The molecular weight of the oligomer is not limited. In general,however, the molecular weight of the oligomer in its uncured state isusually between about 200 and about 10,000, preferably between about 500and about 5,000. Molecular weight as used throughout this disclosuregenerally means number average molecular weight when measured, or thetheoretical calculated molecular weight based on the reactants andreaction conditions used to make the composite oligomer.

There is no particular limitation on the molecular architecture of thecomposite oligomer, although in general, linear or substantially linearoligomeric structures are used rather than non-linear, cyclic, orbranched structures. To the extent that the inventive concept can bepracticed, however, branched or other non-linear structures are alsoenvisioned and are not excluded. A substantially linear structure meansthat there is a single, dominant linear oligomeric backbone which is“capped” at the two ends of the backbone. The amount of branching unitsin the backbone is generally less than about 10 mole %, and preferably,less than about 5 mole %. The linear backbone may contain one or moretypes of repeat units, although preferably, one major type of repeatunit is used. Nevertheless, block or random copolymeric structures canbe used if necessary. With a substantially linear backbone, the numberof branch points in the backbone will be kept to a minimum, andpreferably, will not be used. Synthetic simplicity in the oligomerstructure is preferred to the extent that cost-performance can beachieved.

The term “glass coupling moiety” can be readily understood by a personskilled in the art and is understood to mean a functional group which isknown or has the ability to improve adhesion to an inorganic surface orat an inorganic-organic interface, and in particular, a glass surface orat a glass-polymer interface. Such glass coupling moieties areassociated with conventional coupling agents or adhesion promoters, asknown to those skilled in the art. These conventional coupling agentsgenerally have (1) an organic functional group which bonds with, or isat least associated with, the organic material at the interface, and (2)an inorganic component which bonds, usually covalently, to the inorganicmaterial at the interface. Although the complexities of such bonding arenot fully understood, usually, bonding to the inorganic surface occursfollowing hydrolysis and/or condensation reactions.

Exemplary conventional silane coupling agents are disclosed in E. P.Plueddemann's Silane Coupling Agents, Plenum Press (1982), the completedisclosure of which is hereby incorporated by reference. Non-silanetypes of coupling agents are also known and include, for example,chromium, orthosilicate, inorganic ester, titanium, and zirconiumsystems. Although the present invention is preferably practiced with useof silane glass coupling moieties, the invention is not so restricted,and a person skilled in the art is enabled by the present disclosure touse these other systems as well.

In the present invention, the glass coupling moieties are not part of aconventional coupling agent, but are incorporated covalently into theoligomer in a manner which preserves their coupling function to theinorganic surface or at the inorganic-organic interface. In a preferredembodiment, for example, the organic component of a conventionalcoupling agent is linked covalently, either directly or indirectly, withthe composite oligomer together with the slip agent and radiationcurable moieties. After this linkage, the glass coupling moiety willstill have its inorganic component effective for bonding with theinorganic surface or at the inorganic-organic interface. However, theinvention is not so limited, and the glass coupling moiety is notnecessarily linked to the composite oligomer by reaction of the organicfunctional group of a conventional coupling agent.

Silane coupling moieties are preferred. These moieties can be created bycovalently linking a conventional coupling agent or adhesion promoterwith the oligomer. Representative types of silane coupling moieties havebeen disclosed in the aforementioned Plueddemann reference and theproduct information publication from Union Carbide entitled “UNIONCARBIDE® Organofunctional Silanes Products and Applications” (1991,1992), the complete disclosure of which is hereby incorporated byreference. The inorganic component of the conventional silane couplingagent is generally represented by the formula:

 —Si(OR)₃

where R is a conventional lower, and preferably, a C₁-C₄, alkyl groupsuch as methyl or ethyl which imparts at least some hydrolyzability tothe silane. Other types of R groups are also known in the art, however,and the invention is not particularly limited by the particular R groupor silane structure to the extent that glass coupling can occur.Generally, at least one hydrolyzable “—Si—O—R” linkage will be presentin the glass coupling moiety to facilitate coupling to the surface ofthe optical glass fiber. Preferably, there is more than one suchlinkage. Hydrolyzable means that this linkage is sensitive to reactionwith water to generate “—Si—OH” linkages. In turn, “—Si—OH” linkages arebelieved to condense to form “—Si—O—Si—” linkages. In many cases,hydrolysis may even begin to occur with exposure to atmosphericmoisture. Hydrolysis of silanes and glass surfaces in the context ofoptical fiber coatings is discussed in, for example: (i) the chapterentitled “Coating and Jackets”, Chapter 10, Blyler et al. Optical FiberTelecommunications, 1979, pgs. 299-341, and (ii) S. Wu, PolymerInterface and Adhesion, Marcel Dekker, 1982, pgs. 406-434, the completedisclosures of which are hereby incorporated by reference.

Common organic functionalities of the silane coupling agents include,for example, amino, epoxy, vinyl, methacryloxy, isocyanato, mercapto,polysulfide, and ureido. Using synthetic methods known in the art, theorganic functionality can be reacted with the oligomer to yield acovalent linkage between the glass coupling moiety and the oligomer. Ina preferred embodiment, for example, mercaptopropyl silane is linkedwith an oligomer containing an isocyanate group to form a thiourethaneadduct between the mercapto group and the isocyanate group. Although astrong linkage is preferred, the present invention encompasses thepossibility that although a covalent linkage is formed, the covalentlinkage may not be strong and may, for example, be sensitive todisruption with the application of heat. However, as long as the glasscoupling moiety produces the desirable effect of promoting adhesion, thecovalent linkage is sufficient. If necessary, catalysts may be used topromote linkage formation.

Slip agents when used to practice this invention do not substantiallyaffect the adhesion of the inner primary coating to the surface of theoptical glass fiber. Instead, the slip agents reduce the sliding forceof the inner primary coating against the surface of the optical glassfiber, once the bonds between the surface of the optical glass fiber andinner primary coating are broken (i.e. after the inner primary coatinghas been delaminated).

Slip agents are also known in the art as, among other things, release,antiblocking, antistick, and parting agents. Slip agents are commonlyoligomeric or polymeric and are usually hydrophobic in nature, with themost common examples including silicones (or polysiloxanes),fluoropolymers, and polyolefins. If desired, the slip agent moiety caninclude silicones, fluoropolymers, and/or polyolefins in combinationwith polyesters, polyethers and polycarbonates. Slip agents aredisclosed in, for example, the article entitled “Release Agents”published in the Encyclopedia of Polymer Science, 2nd Ed., Vol. 14,Wiley-Interscience, 1988, pgs. 411-421, the complete disclosure of whichis hereby incorporated by reference. Although slip agents operate over awide variety of interfaces, the present invention is particularlyconcerned with an interface of a glass surface, and in particular, aglass-organic coating interface between the inner primary coating andthe surface of the optical glass fiber. A slip agent can be covalentlyincorporated into the composite oligomer as a slip agent moiety.

In a preferred embodiment, the slip agent moiety is the principalcomponent of the oligomer in terms of weight percent because the slipagent moiety itself is usually oligomeric in nature, and the glasscoupling and radiation-curable moieties are usually of lower molecularweight. For example, the slip moiety can be up to about 95 wt. % of thetotal composite oligomer weight when the three moieties are directlylinked together. However, when an oligomeric backbone is present, theslip agent usually can be up to about 85 wt. % of the composite oligomerweight. As with the molecular weight of the composite oligomer of thepresent invention, the molecular weight of the slip agent moiety is notstrictly limited, but will generally be between about 150 and about9,500, preferably, between about 400 and about 4500.

As with the molecular architecture of the oligomer, there is noparticular limitation on the molecular architecture of the slip agentmoiety, although in general, substantially linear structures can beused. Non-linear or branched structures, however, are not excluded.Oligomeric slip agent moieties, when present, may contain differentkinds of repeat units, although preferably, there is one main type ofrepeat unit.

Oligomeric silicone slip agent moieties are preferred, and oligomericsilicones comprising substantial portions of methyl side groups areparticularly preferred. The side groups preferably impart hydrophobiccharacter to the silicone. Other preferred side groups include ethyl,propyl, phenyl, ethoxy, or propoxy. In particular, dimethylsiloxanerepeat units represented by the formula, “—OSi(CH₃)₂—” are preferred.

In a preferred embodiment, the end groups on a substantially linearsilicone oligomer can be linked with a radiation curable moiety at oneend and a slip agent moiety at the other end. Such linkage can involveintermediate linkage groups. Although linkage at the silicone oligomerend group is preferred, the silicone moiety can be tailored for linkagewith slip agent and radiation-curable moieties at other points in theoligomer molecule besides the end groups. For example, functional groupscan be incorporated throughout the molecular structure of the siliconeoligomer that are linked with the radiation-curable and slip agentmoieties. Examples of functionalized silicones which can be incorporatedinto the oligomer include polyether, polyester, urethane, amino, andhydroxyl.

Other types of slip agent moieties including those made from fluorinatedslip agents can also be used. Examples of suitable fluorinated slipagents include FC-430, FX-13, and FX-189 (Minnesota Mining andManufacturing), Fluorolink E (Ausimont), and EM-6 (Elf Atochem).

Generally, the composite oligomer of the present invention is surfaceactive because of the glass coupling moieties, and in particular, maytend to concentrate at coating interfaces, such as the glass-coatinginterface, if not bound in the inner primary coating. However, thecovalent binding of the composite oligomer after cure, due to theradiation-curable moiety, may retard such surface activity or migration.Surface activity means that the composite oligomer, when placed in aformulation, tends to migrate to the surface of the formulation ratherthan be dispersed evenly throughout the formulation.

The radiation-curable moiety should help ensure that the compositeoligomer is covalently linked within a radiation-curable coating so thatthe composite oligomer cannot be extracted or volatilized from the curedcoating without breaking covalent bonds.

The radiation-curable moiety can include any functional group capable ofpolymerizing under the influence of, for example, ultraviolet orelectron-beam radiation. One type of radiation-curable functionality is,for example, an ethylenic unsaturation, which in general is polymerizedthrough radical polymerization, but can also be polymerized throughcationic polymerization. Examples of suitable ethylenic unsaturation aregroups containing acrylate, methacrylate, styrene, vinylether, vinylester, N-substituted acrylamide, N-vinyl amide, maleate esters andfumarate esters. Preferably, the ethylenic unsaturation is provided by agroup containing acrylate, methacrylate or styrene functionality. Mostpreferably, the ethylenic unsaturation is provided by a group containingacrylate functionality.

Another type of functionality generally used is provided by, forexample, epoxy groups, or thiol-ene or amine-ene systems. Epoxy groups,in general, can be polymerized through cationic polymerization, whereasthe thiol-ene and amine-ene systems are usually polymerized throughradical polymerization. The epoxy groups can be, for example,homopolymerized. In the thiol-ene and amine-ene systems, for example,polymerization can occur between a group containing allylic unsaturationand a group containing a tertiary amine or thiol.

The amount or number of glass coupling, slip agent, and radiationcurable moieties in the composite oligomer is not particularly limitedprovided that advantages of the present invention can be achieved andthe inventive concept is practiced. Thus, a single molecule of thecomposite oligomer can contain multiple numbers of glass coupling, slipagent, or radiation-curable moieties, although in a preferredembodiment, a single oligomeric molecule contains one glass coupling,one slip agent, and one radiation-curable moiety.

The glass coupling, slip agent, and radiation curable moieties should becovalently linked together in the oligomer. There is no particularlimitation to how this linkage is effected provided that advantages ofthe present invention are achieved and the inventive concept practiced.Linkage may entail direct linkage to the oligomer, or alternatively,indirect linkage to the oligomer. Intermediate linking groups willgenerally operate by way of two functional groups on a linking compoundwhich can link, for example, the radiation-curable moiety with the slipagent moiety, or link the glass coupling moiety with the slip agentmoiety.

Representative linking compounds include diisocyanate compounds, whereinlinkage occurs by formation of urethane, thiourethane; or urea links byreaction of hydroxyl, thiol, and amino groups respectively, withisocyanate. Such diisocyanate compounds are well-known in thepolyurethane and radiation curable coating arts. Aromatic or aliphaticdiisocyanates can be used, although aliphatic diisocyanates arepreferred. Other linkages can be through, for example, carbonate, etherand ester groups. Preferably, urethane, urea or thiourethane groups areused as the linking groups.

The oligomer, therefore, preferably comprises within its structure atleast one linkage represented by

 —NH—CO—X—

wherein X is an oxygen, sulfur, or nitrogen atom. Urethane andthiourethane groups are most preferred. Urethane groups, for example,can hydrogen bond.

Although the present invention is not limited to one particularmolecular architecture for the composite oligomer, in a preferredembodiment which makes use of intermediate linking groups, the compositeoligomer can be represented by the following generic structure:

R—L₁—A—L₂—C

wherein A represents the slip agent moiety,

R represents a radiation-curable moiety,

C represents the glass coupling moiety, and

L₁ and L₂ represent linking groups.

L₁ and L₂ can be independently any group capable of providing a covalentlink between the “R” moiety and the “A” moiety or between the “C” moietyand the “A” moiety. Based on the disclosure provided herein, one skilledin the art will easily be able to understand what linking groups aresuitable for the particular “A”, “C” and “R” groups selected.

In particular, urethane and thiourethane groups are preferred. Urethaneand thiourethane linking groups are formed by, for example, (i) linkinga hydroxyl end-capped oligomer with a low molecular weight diisocyanatecompound at both oligomer ends without extensive coupling of theoligomer, (ii) linking the isocyanate end-capped oligomer with a lowmolecular weight hydroxyacrylate compound, or (iii) linking theisocyanate end-capped oligomer with a low molecular weight mercaptocompound.

The linking groups, however, are considered optional. In other words,the oligomer also can be represented by the following genericstructures:

R—L₁—A—C,

R—A—L₂—C, or

R—A—C.

Although the present invention is disclosed in terms of theaforementioned groups or moieties, other groups can in principle beincorporated into the molecular structure to the extent that theadvantages of the present invention can be achieved and the inventiveconcept practiced.

A preferred embodiment of the present invention is the preparation of acomposite oligomer with use of the following ingredients: a siliconeoligomer having two hydroxyl end groups (slip agent moiety), isophoronediisocyanate (linkage), hydroxyethyl acrylate (radiation-curablemoiety), and mercaptopropyl silane (glass coupling moiety). Isophoronediisocyanate (IPDI) serves to end-cap both ends of the silicone diololigomer and provide a linking site with the hydroxyethyl acrylate atone end of the silicone oligomer and with the mercaptopropyl silane atthe other end.

A preferred application for the composite oligomer is as an oligomericadditive, or even as a main oligomeric component, in a radiation-curablecoating, and in particular, an inner primary, optical glass fibercoating. The amount of oligomeric additive incorporated into theradiation curable matrix is not particularly limited but will besufficient or effective to achieve the specific performance objectivesof the particular application. In general, however, a suitable amountwill be between about 0.5 wt. % and about 90 wt. %, preferably, betweenabout 0.5 wt. % and about 60 wt. %, and more preferably, between about0.5 wt. % and about 30 wt. % with respect to the total weight of theradiation-curable coating formulation. In general, higher molecularweight composite oligomers will be present in a radiation-curablecoating in greater weight percentages than lower molecular weightcomposite oligomers.

The composite oligomer functions to tailor the properties offormulations which exhibit too great a coefficient of friction or toolow adhesion. Specifically, the composite oligomer can increase theadhesion if the adhesion is unacceptably low, and in particularunacceptably low in the presence of moisture. Alternatively, thecomposite oligomer can reduce the coefficient of friction of a coating.Conventional coupling additives and slip agents cannot perform this dualfunction.

If desired, although a reduction in the number of additives isdesirable, the composite oligomer can be used in conjunction withconventional coupling and slip agents to improve absolute performance orcost-performance. In a preferred embodiment, for example, the compositeoligomeric can be used in conjunction with a functional organosilanecompound such as, for example, mercaptopropyl silane. For example, ahydroxybutylvinylether adduct with OCN—(CH₂)₃Si(OCH₃)₃ can also be usedtogether with the composite oligomer.

The composite oligomer can be incorporated into a wide variety ofradiation-curable formulations. There are no particular limitationsprovided that the inventive concept is practiced and advantages accrue.One skilled in the art of formulating radiation-curable coatings willeasily be able to incorporate the composite oligomer therein to providethe desired properties.

In optical glass fiber coating applications, for example, otherformulation components generally include:

(i) at least one multi-functional radiation-curable oligomer, which is adifferent oligomer than the composite oligomer of the present invention,to provide a cross-linked coating;

(ii) at least one reactive diluent to adjust the viscosity to a levelacceptable for application to optical glass fibers, and

(iii)at least one photoinitiator.

Additives such as antioxidants, and as already noted, coupling and slipagents may also be utilized.

Radiation-curing is generally rapidly effected with-use of ultravioletlight, although the present invention is not so limited, and a person ofskill in the art can determine the best cure method. Radiation-curingresults in polymerization of at least some of the radiation-curablemoieties present in the composite oligomer which covalently links thecomposite oligomer to itself or, more preferably, otherradiation-curable components in the formulation. The chemical processeswhich occur upon mixing and curing formulations are in some casescomplex and may not be fully understood. The present invention, however,is not limited by theory and can be readily understood and practiced bypersons of skill in the art. The formulations of the present invention,just like the composite oligomer, can be in pre-cured, partially cured,and in cured states. The term component, which defines additives andcompounds used to prepare the formulations, generally refers to startingmaterials before mixing. After mixing, interactions or even reactionsbetween the components may occur.

The composite oligomer can be incorporated into inner primary coatingcompositions, outer primary coating compositions, ink compositions andmatrix forming compositions. The composite oligomer also can beincorporated into so-called single coating systems.

In general, the coating substrate will be an inorganic or glasssubstrate, although in principle, other substrates such as polymericsubstrates may also be effectively used. The substrate preferably hasthe capacity to couple with the glass coupling moiety of the oligomericadditive. In a preferred application, the coating substrate is anoptical glass fiber, and in particular, a freshly drawn, pristineoptical glass fiber. Freshly prepared optical glass fiber is known inthe art to be responsive to glass coupling agents. Exemplary methods ofcoating optical fibers are disclosed in, for example, U.S. Pat. Nos.4,474,830 and 4,913,859, the complete disclosures of which are herebyincorporated by reference.

The present inventions will be further explained by use of the followingnon-limiting examples.

EXAMPLE 2-1 Comparative Examples B-1 and B-2

Synthesis of Novel Composite Oligomer

A 1,000 mL four-necked flask was charged with isophorone diisocyanate(55.58 g). 2,6-di-tertbutyl-4-methylphenol (0.12 g) and dibutyltindilaurate (0.24 g) were added to the flask. 14.51 grams of Hydroxyethylacrylate was added over a 90 minute period while maintaining thetemperature below 40 C. At the end of 90 minutes, the temperature wasincreased to 40 C., and the mixture was stirred at 40 C. for one hour.The temperature was allowed to decrease to about 30 C. Mercaptopropylsilane (28.13 g of an 87.1% pure product) was added over 90 minutesduring which time the temperature was maintained below 40 C. After theaddition of mercaptopropyl silane, the temperature was increased to 40C., and the reaction mixture was stirred at 40 C. for 17-18 hours. 300 gof a 50% ethoxylated polydimethylsiloxane diol of 1200 equivalent weightQ4-3667 (Dow Corning) was then added, and the temperature was increasedto 70 C. After about six hours, the isocyanate content was measured tobe about zero percent. The temperature was decreased to 50 C. Based onthe reaction conditions and reactants, a composite silicone silaneacrylate oligomer was formed having the following structure:

H—I—(Q4-3667)—I—M

wherein:

H=hydroxyethylacrylate,

I=isophorone diisocyanate,

Q4-3667=the above described silicone diol, and

M=mercaptopropyl silane

Preparation of Pre-cured Formulation

The components shown in Table 2 were combined, except for the compositeoligomer and the silane coupling agent. The components were heated toabout 60 C. and mixed to form homogeneous mixtures. The compositeoligomer and silicone coupling agent were mixed therein and the mixturewas heated for approximately 15 minutes at 60 C. to form an improvedradiation-curable, inner primary, optical glass fiber coatingcomposition, Example 2-1. The mixtures for Comparative Examples B-1 andB-2 were prepared similarly. Drawdowns of the compositions were made andthen suitably cured by exposure to UV light to form cured coatings. Thecured coatings were tested for resistance to delamination and fiberpull-out residue using the following methods.

Water Soak Delamination Test

A drawdown of each inner primary coating composition was made to form a75 micron film of the inner primary coating composition on microscopeslides and then cured by exposure to 1.0 J/sq cm, from a Fusion D lamp,120 W/cm, under a nitrogen atmosphere. Then, a drawdown of each outerprimary coating was made to form a 75 micron film of the outer primarycoating composition over the cured 75 micron inner primary film, andthen cured in the same manner as the inner primary coating.

Deionized water was placed in a 500 ml beaker and the coated microscopeslides were soaked in the water. The beaker containing the coated slideswas then placed in a 60 C. hot water bath. The films were observed fordelamination periodically. The time when the first signs of delaminationappeared were recorded.

Fiber Pull-out Residue Test

The operation of stripping coatings from optical fibers to leave a bareglass surface was simulated by pulling four bare glass fibers out of alayer of cured inner primary coating. Microscopic examination of thepulled-out fibers at low magnification (e.g., 10×) clearly revealed thepresence or absence of debris on the glass surface. If debris waspresent, the amount of debris was noted. The results of these tests areprovided in Table 2.

TABLE 2 Comp. Ex Comp. Ex Ex. 2-1 B-1 B-2 Component (Amount is % byweight based on total weight of composition) Urethane acrylate 53.2 5653.87 oligomer Isodecyl Acrylate 13.3 14 13.47 Ethoxylated-nonylphenol24.22 25.5 24.53 Monoacrylate Silicone Silane 5 0 0 OligomerH-I-Q4-3667-I-A189 Q4-3667 (Dow Corning) 0 0 3.8 Photoinitiator 2.85 32.89 Antioxidant 0.47 0.5 0.48 y-Mercapto-propyl 0.95 1.0 0.96Trimethoxy-Silane Fiber no lot of no Pull-out Residue Test residueresidue residue Delamination, none none delam. if any, after After 1 thehot water hour at soak* 60° C. The oligomers were formed by reacting thefollowing monomers: H = Hydroxyethyl Acrylate I = IsophoroneDiisocyanate Q4-3667 = ethoxylated polydimethylsiloxane diol, MW of 1200(Dow Corning) *Samples were aged for 4 hours at 60° C. Then the waterbath was shut-off for about 70 hours. The temperature was then broughtback to 60° C. for an additional 48 hours.

Comparative Example B-1 was a formulation which did not contain thecomposite oligomer of the present invention, but which contained asilane coupling agent. However, poor results were obtained in thepull-out test because adhesion was too strong.

Comparative Example B-2 was a formulation which contained a conventionalsilicone slip agent. The silicone slip agent improved the results of thepull-out test compared to Comparative Example A, but only at the expenseof hydrolytic interfacial adhesion.

Example 2-1 was a formulation that contained the composite oligomer ofthe present invention. The composite oligomer remarkably improved theresults of the pull-out test but not at the expense of hydrolyticinterfacial adhesion.

Examples 2-2 and 2-3 Comparative Examples B-3 and B-4

These Examples and Comparative Examples were conducted to demonstratethe effect of the composite oligomer on glass plate adhesion. Theformulations shown in Table 3 were prepared in the same manner as inExample 2-1 and Comparative Examples B-1 and B-2. The silicone silaneacrylate oligomer was prepared in the same manner as in Example 2-1,except that a silicone diol HSi-2111 (Tego Chemie) was used instead ofQ4-3667 (Dow Corning).

Films of the coating materials (75 microns thick) were prepared onmicroscope slides and then cured by exposure to UV light. A commerciallyavailable outer primary coating was formed on top of the coatings. Thefilms were soaked in water at 60 C. and then examined for delamination.In addition, dry and wet adhesion was measured at 50% and 95% relativehumidity (RH), respectively. The results are summarized in Table 3.

Dry (50% RH) and wet (95% RH) adhesion can be measured by recognizedtest methods. For example, as explained in U.S. Pat. Nos. 5,336,563(Coady et al.) and 5,384,342 (Szum), the wet and dry adhesion was testedon cured film samples prepared by drawing down, with a Bird Bar, a 75micron film of the coating compositions on glass microscope slides andcured by exposure to 1.0 J/sq cm, from a Fusion D lamp, 120 W/cm, undera nitrogen atmosphere, as noted above in Example 2-1.

The samples were then conditioned at a temperature of 23±2° C. and arelative humidity of 50±5% for a time period of 7 days. A portion of thefilm was utilized to test dry adhesion. Subsequent to dry adhesiontesting, the remainder of the film to be tested for wet adhesion wasfurther conditioned at a temperature of 23±2° C. and a relative humidityof 95% for a time period of 24 hours. A layer of polyethylene wax/waterslurry was applied to the surface of the further conditioned film toretain moisture.

The adhesion test was performed utilizing apparatus which included auniversal testing instrument, e.g., an Instron Model 4201 commerciallyavailable from Instron Corp., Canton, Mass., and a device, including ahorizontal support and a pulley, positioned in the testing instrument.

After conditioning, the samples that appeared to be uniform and free ofdefects were cut in the direction of the draw down. Each sample was 6inches long and 1 inch wide and free of tears or nicks. The first oneinch of each sample was peeled back from the glass. The glass wassecured to the horizontal support with the affixed end of the specimenadjacent the pulley. A wire was attached to the peeled-back end of thesample, run along the specimen and then run through the pulley in adirection perpendicular to the specimen. The free end of the wire wasclamped in the upper jaw of the testing instrument which was thenactivated. The test was continued until the average force value, ingrams force/inch, became relatively constant. The preferred value forwet adhesion is at least about 5 g/in.

TABLE 3 Comp. Ex. Comp. Ex. Ex. 2-2 Ex.2-3 B-3 B-4 Component (Amount isparts by weight) Oligomer C 49.22 49.22 49.22 49.22 H-I-(PTHF2000-I)₂- HEthoxylated 24.76 24.76 24.76 24.76 nonylphenol Acrylate Lauryl Acrylate16.64 16.64 16.64 16.64 2,4,6- 3.0 3.0 3.0 3.0 trimethylbenzoylD-iphenyl Phosphine Oxide Thiodiethylene 0.46 0.46 0.46 0.46 bis(3,5-di-Tert- Butyl-4- Hydroxy)hydrocinn- amate gamma- 0.92 — 0.92Mercaptopropyl Trimethoxy Silane Silicone Silane 5 5 — — AcrylateOligomer H-I-HSi2111-I-M Adhesion at 50% 45 14 27 9 RH (g/in) Adhesionat 95% 34 12 20 4 RH (g/in) 60 C Water Soak No Slight No DelaminatDelamin Delamin Delaminati ion After ation ation on After 8 15 AfterAfter Hours; Minutes 24 15 Slight Hours Minutes Delaminati on After 24Hours The oligomers were formed by reacting the following monomers: H =Hydroxyethyl Acrylate I = Isophorone Diisocyanate M = Mercapto SilanePTHF2000 = 2000 molecular weight Polytetramethylene Ether Glycol (BASF)HSi2111 = a silicone dial having a MW of 1000 (Tego Chemie)

The results in Table 3 indicate that the composite oligomer is not onlyable to improve adhesion to the glass surface, but is also able to actsynergistically with a conventional silane coupling agent.

EXAMPLE 2-4

The formulation shown in Table 4 was prepared in the same manner as inExample 2-1. The silicone silane acrylate oligomer was the same as thatprepared in Example 2-1.

A film of the coating material (75 micron thick) was prepared on glassplates and then cured by exposure to UV light in the same manner asabove. The tensile strength, elongation and modulus were measured.

A 75 micron film of the coating material was also prepared and suitablycured. The crack propagation was then measured. A fiber pull-outfriction test was also conducted, as described herein. The predictedribbon strip cleanliness was calculated. The results are shown in Table4.

TABLE 4 Example 2-4 Component (Amount in % by weight of totalcomposition) H-I-(PTGL2000-I),-H 49.24 Ethoxylated Nonylphenol AcrylateEster 25.46 Diphenyl (2,4, 6-trimethylbenzoyl) Diphenyl 3 PhosphineOxide and 2-Hydoxy-2-Methyl-1- Phenyl-l-Propanone blend Lauryl Acrylate16 Thiodiethylene bis (3,5-di-Tert-Butyl-4- 0.5 Hydroxy)hydrocinnamateH-I-HSi2111-I-M 5 Mercaptopropyl trimethoxy silane 0.8 Test ResultsViscosity, mPa.s at 25 C. 7000 Tensile Strength, MPa 0.8 Elongation, %230 Modulus, MBa 1 Dose@95% Modulus, J/cm² 0.64 E′=100 MPa, ° C. −66E′=100 MPa, ° C. −50 Peak TAN Delta ° C. −40 E₀, MPa 1.3 StripCleanliness Predicted 3 Crack Propagation, mm 1.49 Fiber Pull-outFriction, g/mm 18.5 The oligomers were formed by reacting the followingcomponents: H = Hydroxyethyl Acrylate I = Isophorone Diisocyanate M =Mercaptopropyl trimethoxy silane PTGL2000 = 2000 molecular weightpolymethyltetrahydrofurfuryl/polytetrahydrofurfuryl copolymer diol(Mitsui, NY) HSi2111 = a silicone diol having a MW of 1000 (Tego Chemie,or Gold Schmidt Chemical Corp.)

From the above test data, surprisingly, the novel silicon silaneacrylate oligomer can be used to provide an inner primary coating havinga fiber friction that provides a resistive force that is less than thecohesive strength of the inner primary coating. This finding is based onthe predicted strip cleanliness being about 3. A value of about 3 orless is very good and will usually provide a bare optical glass fiberwhich is suitable for connection to another optical glass fiber orcomponent of a light transmission assembly, without having to wiperesidue from the bare optical glass fiber.

Description of Test Methods Used Herein

Predicted Strip Cleanliness Test Method

The predicted strip cleanliness is the predicted degree of cleanlinessof a bare optical glass fiber after the inner primary coating has beenremoved during ribbon stripping. A lower number is better.

Surprisingly, it has been found that the degree of cleanliness of a bareoptical glass fiber of a selected ribbon assembly can be predicted bymeasuring the following two properties of the inner primary coating:

(1) fiber pull-out friction; and

(2) crack propagation.

The crack propagation is a measure of the cohesive strength of the innerprimary coating. The greater the cohesive strength of the inner primarycoating the greater the amount of energy required to break apart theinner primary coating. Thus, an inner primary coating having a highercohesive strength can withstand greater stripping forces during ribbonstripping without breaking apart and leaving residue on the surface ofthe optical glass fiber, than an inner primary coating having a lowercohesive strength.

The crack propagation can be measured as follows. First make a 75 micronthick drawdown of the inner primary composition and then cure the filmby exposing it to 1.0 J/cm² of UV from a Fusion D lamp under a nitrogenatmosphere. Cut three test strips of dimensions 35 mm long, 12 mm wide,and 75 micron thick. A cut 2.5 mm long is made in the side of eachstrip. A strip is mounted in a RSA-II rheometer, the temperature broughtto 90 C. (representative ribbon stripping temperature), and a constantextension rate of 0.1 mm/second is applied to the test strip. Themeasure of cohesive strength is the increase in length L before thecrack propagates across the width of the test strip. The gauge length isconstant at 23.2 mm. The value reported is currently the average ofthree measurements.

The fiber pull-out friction of the inner primary coating is an estimateof the fiber friction between the inner primary coating and the bareoptical glass fiber. In general, the lower the fiber pull-out frictionof the inner primary coating the lower the fiber friction between theoptical glass fiber and the inner primary coating, the lower theresistive force, and the easier the inner primary coating will slide offof the optical glass fiber. Also, the lower the fiber friction, the lessforce that will be applied to the inner primary coating to conductribbon stripping. The less the force being applied to the inner primarycoating, the lower the chance that the cohesiveness of the inner primarycoating will fail, thus leaving inner primary coating residue on thesurface of the optical glass fiber.

The fiber pull-out friction test can be performed as follows. The sampleconsists of a bare, clean optical fiber, one end of which has beenembedded in a 250 micron thick sheet of cured inner primary coating tobe tested. This assembly is mounted in a suitable instrument such as aRheometrics RSA-II rheometer, and the temperature raised to arepresentative ribbon stripping temperature (such as 90° C.), and thefiber pulled slowly out of the sheet at a rate of 0.1 mm/sec. Theinstrument records and plots force vs distance. The plots typically showa linear region of negative slope, which is the result of a decreasingarea of contact between fiber and coating, as the fiber is beingwithdrawn. The slope is measured, and is the output of the test. Lowslope values correspond to a low fiber pull-out friction, and viceversa. Three test samples should be performed and their average used asthe final output of the test.

Prior to using the information from the crack propagation andcoefficient of friction measurements as a prediction method, calibrationis required. Calibration consists of obtaining test data on at leastfive inner primary coatings of known cleanliness performance, andfitting the data to a three-dimensional surface using statisticalprocedures in a suitable statistical/plotting computer program. Aconvenient two-dimensional representation of the three-dimensionalsurface is a contour plot, in which each contour represents a fixedvalue of the cleanliness rating, and the vertical and horizontal axesare output values of the fiber pull-out friction and crack propagationtests, respectively.

The cleanliness ratings should be expressed on a quantitative scale, forexample, a scale of 1 to 5. An example of a suitable quantitative scaleis the “Mill's” test described in the background section herein above,the complete disclosure of which is incorporated herein by reference.When referring to strip cleanliness and predicted strip cleanlinessherein, the numerical values correspond to those of the Mill's test.

After the calibration contour plot has been obtained, a point is plottedon it, using data from crack propagation and fiber pull-out frictionmeasurements of an inner primary coating formulation for which acleanliness prediction is desired. A prediction of cleanliness isobtained by noting the position of the point relative to the contourlines closest to it.

The following hypothetical example illustrates the calibration step, andthe use of the contour plot thus produced, to obtain a predictedribbon-stripping cleanliness. Eight inner primary coatings A through H,are prepared, and coated on an optical fiber in the usual manner, allhaving the same outer primary coating over the respective inner primarycoatings. Coated fiber representing each of the eight inner primarycoatings are then coated with an ink layer, and then assembled into aribbon assembly. The type of ink and matrix material for ribbon assemblyshould be identical for all eight specimens. Three ribbon assemblies ofeach sample can be stripped at the desired ribbon stripping temperature.The cleanliness of each sample is evaluated using the Mill's test, inwhich 1 is best and 5 is worst. The final rating for each of the eightspecimens is the average of the ratings of the three replicates. Thehypothetical results are shown in Table 5.

TABLE 5 (HYPOTHETICAL) Fiber Crack Friction Propagation Coating (g/mm)(mm) Rating A 2 1.1 1.6 B 30 0.8 5 C 35 1.6 3.7 D 20 1.7 2.8 E 7 2.3 1.8F 25 2.0 1.5 G 4 1.6 1.6 H 22 1.0 3.9

Next, samples for fiber pull-out friction and crack propagation areprepared from the inner primary coating made from the selected innerprimary composition, and output values for each test obtained, by themethods described herein. At this point, there are three data valuesassociated with each of the eight samples. Hypothetical values, chosento be typical of actual cases, are recorded in Table 5. The contour plotproduced by a statistical software program is shown in FIG. 6.

This contour plot is used as follows. For example, a sample of anexperimental inner primary coating is measured by the Fiber Pull-OutFriction and Crack Propagation tests, and the resulting data values were10 and 1 respectively. The point corresponding to those values islocated on the contour plot, and it is seen to fall between the contourvalues of 2.5 and 3. From its location relative to the two lines, thepredicted cleanliness rating is estimated to be about 2.7.

A value of about 3 or less is considered acceptable for optical glassfiber connections.

Viscosity Test Method

The viscosity was measured using a Physica MC10 Viscometer. The testsamples were examined and if an excessive amount of bubbles was present,steps were taken to remove most of the bubbles. Not all bubbles need tobe removed at this stage, because the act of sample loading introducessome bubbles.

The instrument was set up for the conventional Z3 system, which wasused. The samples were loaded into a disposable aluminum cup by usingthe syringe to measure out 17 cc. The sample in the cup was examined andif it contains an excessive amount of bubbles, they were removed by adirect means such as centrifugation, or enough time was allowed toelapse to let the bubbles escape from the bulk of the liquid. Bubbles atthe top surface of the liquid are acceptable.

The bob was gently lowered into the liquid in the measuring cup, and thecup and bob were installed in the instrument. The sample temperature wasallowed to equilibrate with the temperature of the circulating liquid bywaiting five minutes. Then, the rotational speed was set to a desiredvalue which will produce the desired shear rate. The desired value ofthe shear rate is easily determined by one of ordinary skill in the artfrom an expected viscosity range of the sample.

The instrument panel read out a viscosity value, and if the viscosityvalue varied only slightly (less than 2% relative variation) for 15seconds, the measurement was complete. If not, it is possible that thetemperature had not yet reached an equilibrium value, or that thematerial was changing due to shearing. If the latter case, furthertesting at different shear rates will be needed to define the sample'sviscous properties. The results reported are the average viscosityvalues of three test samples.

Tensile Strength, Elongation and Modulus Test Method

The tensile strength, elongation and modulus of cured samples was testedusing a universal testing instrument, Instron Model 4201 equipped with apersonal computer and software “Series IX Materials Testing System.” Theload cells used were 2 and 20 pound capacity. The ASTM D638M wasfollowed, with the following modifications.

A drawdown of each material to be tested was made on a glass plate andcured using a UV processor. The cured film was conditioned at 22 to 24°C. and 50±5% relative humidity for a minimum of sixteen hours prior totesting.

A minimum of eight test specimens, having a width of 0.5±0.002 inchesand a length of 5 inches, were cut from the cured film. To minimize theeffects of minor sample defects, sample specimens were cut parallel tothe direction in which the drawdown of the cured film was prepared. Ifthe cured film was tacky to the touch, a small amount of talc wasapplied to the film surface using a cotton tipped applicator.

The test specimens were then removed from the substrate. Caution wasexercised so that the test specimens were not stretched past theirelastic limit during the removal from the substrate. If any noticeablechange in sample length had taken place during removal from thesubstrate, the test specimen was discarded.

If the top surface of the film was talc coated to eliminate tackiness,then a small amount of talc was applied to the bottom surface of testspecimen after removal from the substrate.

The average film thickness of the test specimens was determined. Atleast five measurements of film thickness were made in the area to betested (from top to bottom) and the average value used for calculations.If any of the measured values of film thickness deviates from theaverage by more than 10% relative, the test specimen was discarded. Allspecimens came from the same plate.

The appropriate load cell was determined by using the followingequation:

[A×145]×0.0015=C

Where: A=Product's maximum expected tensile strength (MPa);

145=Conversion Factor from MPa to psi;

0.00015=approximate cross-sectional area (in²) of test specimens; and

C=lbs.

The 2 pound load cell was used for materials where C=1.8 lbs. The 20pound load cell was used for materials where 1.8<C<18 lbs. If C>19, ahigher capacity load cell was required.

The crosshead speed was set to 1.00 inch/min (25.4 mm/min), and thecrosshead action was set to “return at break”. The crosshead wasadjusted to 2.00 inches (50.8 mm) jaw separation. The air pressure forthe pneumatic grips was turned on and adjusted as follows: setapproximately 20 psi(1.5 Kg/cm²) for primary optical fiber coatings andother very soft coatings; set approximately 40 psi(3 Kg/cm²) for opticalfiber single coats; and set approximately 60 psi(4.5 Kg/cm²) forsecondary optical fiber coatings and other hard coatings. Theappropriate Instron computer method was loaded for the coating to beanalyzed.

After the Instron test instrument had been allowed to warm-up forfifteen minutes, it was calibrated and balanced following themanufacturer's operating procedures.

The temperature near the Instron Instrument was measured and thehumidity was measured at the location of the humidity gage. This wasdone just before beginning measurement of the first test specimen.

Specimens were only analyzed if the temperature was within the range23±1.0 C. and the relative humidity was within 50±5%. The temperaturewas verified as being within this range for each test specimen. Thehumidity value was verified only at the beginning and the end of testinga set of specimens from one plate.

Each test specimen was tested by suspending it into the space betweenthe upper pneumatic grips such that the test specimen was centeredlaterally and hanging vertically. Only the upper grip was locked. Thelower end of the test specimen was pulled gently so that it has no slackor buckling, and it was centered laterally in the space between the openlower grips. While holding the specimen in this position, the lower gripwas locked.

The sample number was entered and sample dimensions into the datasystem, following the instructions provided by the software package.

The temperature and humidity were measured after the last test specimenfrom the current drawdown was tested. The calculation of tensileproperties was performed automatically by the software package.

The values for tensile strength, % elongation, and (secant or segment)modulus were checked to determine whether any one of them deviated fromthe average enough to be an “outlier.” If the modulus value was anoutlier, it was discarded. If there were less than six data values forthe tensile strength, then the entire data set was discarded andrepeated using a new plate.

Elastic Modulus Test Method

The elastic modulus (E′), the viscous modulus (E″), and the tan delta(E″/E′), which is an indication of the material's Tg, of the exampleswere measured using a Rheometrics Solids Analyzer (RSA-11), equippedwith: 1) A personal computer having MS-DOS 5.0 operating system andhaving Rhios® software (Version 4.2.2 or later) loaded; 2) A liquidnitrogen controller system for low-temperature operation.

The test samples were prepared by casting a film of the material, havinga thickness in the range of 0.02 mm to 0.4 mm, on a glass plate. Thesample film was cured using a UV processor. A specimen approximately 35mm (1.4 inches) long and approximately 12 mm wide was cut from adefect-free region of the cured film. For soft films, which tend to havesticky surfaces, a cotton-tipped applicator was used to coat the cutspecimen with talc powder.

The film thickness of the specimen was measured at five or morelocations along the length. The average film thickness was calculated to±0.001 mm. The thickness cannot vary by more than 0.01 mm over thislength. Another specimen was taken if this condition was not met. Thewidth of the specimen was measured at two or more locations and theaverage value calculated to ±0.1 mm.

The geometry of the sample was entered into the instrument. The lengthfield was set at a value of 23.2 mm and the measured values of width andthickness of the sample specimen were entered into the appropriatefields.

Before conducting the temperature sweep, moisture was removed from thetest samples by subjecting the test samples to a temperature of 80 C. ina nitrogen atmosphere for 5 minutes. The temperature sweep used includedcooling the test samples to about −60 C. or about −80 C. and increasingthe temperature at about 1/minute until the temperature reached about 60C. to about 70 C. The test frequency used was 1.0 radian/second.

Soluble Wax

Wax can be added as a slip agent to adjust the fiber friction betweenthe inner primary coating and the surface of the optical glass fiber toa value that results in a resistive force that is less than the cohesivestrength of the inner primary coating. However, conventional waxesexhibit incompatibility problems with inner primary coatings. Many waxesdo not dissolve well in inner primary coatings and therefore they tendto separate out from solution. Furthermore, conventional waxes tend tocause the resulting inner primary coating to be hazy in appearance,which is undesirable. The term “soluble wax” is used herein to designatethose waxes which are sufficiently soluble in the inner primary coatingcomposition at the concentration required to provide the desired levelof fiber friction. The term “wax” is understood to include waxes asdefined in Hawley's “Condensed Chemical Dictionary”, 11th edition, thesaid definition being incorporated herein by reference.

It has been found that by selecting modified waxes or by modifying thewaxes, the incompatibility problems can be substantially avoided. Inselecting a modified wax, the solubility of the modified wax in thedesired inner primary composition should first be considered. Usually,waxes tend to be insoluble in inner primary coating compositions. Thesolubility of the wax in the inner primary coating will depend mainlyupon the following:

(1) the relative polarity of the wax and the polarity of the monomersand oligomers present in the inner primary composition,

(2) the respective types of functional groups present in the wax and themonomers and oligomers present in the inner primary composition, and

(3) the similarity between the molecular structure of the wax and theoligomers or monomers present in the inner primary composition, such asaliphatic/aromatic, unsaturated/saturated, linear/branched, etc.,entities.

For example, the solubility of the wax can be increased by incorporatingfunctional groups which are similar to those present in the oligomers ormonomers present in the inner primary composition. If the inner primarycomposition contains monomers or oligomers having ester groups, thenester groups can be incorporated into the molecular backbone structureof the wax or the ester groups can be grafted onto the backbone of thewax. Alternatively, wax-like, long-chain fatty esters can be used.Commercial examples of suitable fatty esters include:

Laneto-50 and 100 (PEG-75 lanolin),

Laneto-AWS (PPG-12-PEG-50 lanolin),

Ritacetyl (acetylated lanolin),

Ritahydrox (hydroxylated lanolin),

Ritasol (isopropyl lanolate),

Ritalan (lanolin oil),

Ritalan AWS (PPG-12-PEG-65-lanolin oil),

Ritawax (lanolin alcohol),

Supersat (hydrogenated lanolin),

Forlan C-24 (choleth-24 and Ceteth-24),

Ritachol 1000 (cetearyl alcohol, polysorbate 60, PEG-150-stearate, andsteareth-20),

Ritapro 100 (cetearyl alcohol, steareth-20, and steareth-10),

Pationic ISL (sodium isostearoyl lactylate),

Pationic CSL (calcium stearoyl lactylate),

Pationic SSL (sodium stearoyl lactylate),

Pationic SBL (sodium behenoyl lactylate),

Pationic 138C (sodium lauroyl lactylate),

Pationic 122A (sodium caproyl lactylate),

Pationic SCL (sodium cocoyl lactylate),

Ritox 36 (laureth-23),

Ritox 52 (PEG-40 stearate),

Rita CA (cetyl alcohol),

Rita SA (stearyl alcohol), and

Rita Cetearyl Alcohol 70/30, (RITA Corp.). Preferably, the fatty estermodified wax is isocetyl stearate.

If the inner primary composition contains monomers or oligomers havingalkoxy or hydroxy groups, then to increase the solubility of the wax,alkoxy or hydroxy groups can be incorporated into the molecular backbonestructure of the wax or the alkoxy groups can be grafted onto thebackbone of the wax. Commercial examples of such modified waxes includethe Unilin™ series of alcohol modified waxes from Petrolite, and Ritawax(lanolin alcohol),

Ritachol 1000 (cetearyl alcohol, polysorbate 60, PEG-150-stearate, andsteareth-20),

Ritapro 100 (cetearyl alcohol, steareth-20, and steareth-10),

Rita CA (cetyl alcohol),

Rita SA (stearyl alcohol), and

Rita Cetearyl Alcohol 70/30, (RITA Corp.). Preferably, the alkoxymodified wax is

polypropyleneglycol₁₂polyethyleneglycol₅₀lanolin.

As another example, if the inner primary composition contains monomersor oligomers having amine groups, then to increase the solubility of thewax, amine groups can be incorporated into the molecular backbonestructure of the wax or the amine groups can be grafted onto thebackbone of the wax. An example of such a modified wax is the Armeen™series of amine modified waxes (Armak), such as Armeen TD (tallowamine),

Armeen O, OL or OD (oleylamines),

Armeen SD (soyaamine),

Armeen 18 (octadecylamine),

Armeen HT, HTD or 2HT (hydrogenated tallow),

Armeen T or TM-97 (tallowamine),

Armeen 12D (dodecylamine),

Armeen C or CD (cocoamine),

Armeen 16D (hexadecylamine),

Armeen 2C (dicocoamine),

Armeen M2C (methyldicocoamine),

Armeen DM12D (dimethyldodecylamine),

Armeen DMCD or DMMCD (dimethylcocoamine),

Armeen DM14D (dimethyltetradecylamine),

Armeen DM16D (dimehylhexadecylamine),

Armeen DM18D (dimethyloctadecylamine),

Armeen DMHTD (dimethyl(hydrogenatedtallow)amine,

Armeen DMTD (dimethyltallow amine),

Armeen DMSD (dimethylsoyamine) or

Armeen DMOD (dimethyltallow amine). Preferably, the amine substitutedwax is methyl di(hydrogenated tallow)amine.

An example of a further functional group that can be incorporated intothe wax includes carboxylic acids. Suitable examples of saturatedmodified waxes include capric acid, lauric acid, myristic acid, palmiticacid, and stearic acid. Examples of suitable unsaturated waxes includeoleic acid, ricinoleic acid, linoleic acid, and linolenic acid.

The functional groups present on the modified wax do not necessarilyhave to be identical with those present in the oligomers or monomers ofthe inner primary coating composition in order to achieve increasedsolubility. Functional groups having similar properties, such ashydrogen bonding, polarity, etc., can be mixed and matched as desired toincrease solubility.

The solubility of the wax can also be increased by modifying a wax orselecting a wax having a similar molecular structure to that of themonomers and oligomers present in the inner primary composition. Forexample, if the monomers and oligomers contain aromatic groups, the waxcan be selected or modified to contain aromatic groups. If the monomersor oligomers contain substantial amounts of unsaturation, then the waxcan be modified or selected to contain substantial amounts ofunsaturation. Furthermore, if the monomers or oligomers aresubstantially linear, then a substantially linear wax can utilized.Commercial examples of substantially linear waxes include Polymekon,Ceramer 67 and 1608, and Petrolite C-400, CA-11, WB-5, WB-11, and WB-17(Petrolite).

Based on the teachings provided herein, one skilled in the art will beable to modify or select the desired wax, and to use the selected wax inan amount to provide the desired level of fiber friction between theinner primary coating and the surface of the optical glass fiber. Theamount of the wax present in the inner primary composition will dependon (1) the ability of the wax to impart the desired reduction in thefiber friction between the inner primary coating and the surface of theoptical glass fiber, and (2) the solubility of the wax in the innerprimary composition. The greater the solubility of the wax in the innerprimary composition, the greater the amount of wax that can be present.The greater the ability of the wax to reduce fiber friction, the lesswax that will be required. Preferably, the amount of wax present isabout the minimum amount necessary to provide a level of fiber frictionnecessary to result in a resistive force that provides a clean, residuefree optical glass fiber after ribbon stripping. As discussed above, thefiber friction level that results a resistive force level which willprovide a clean, optical glass fiber after ribbon stripping depends onthe cohesive strength of the inner primary coating. The greater thecohesive strength of the inner primary coating, the greater the amountof resistive force that can be tolerated and still provide a clean, bareoptical glass fiber after ribbon stripping. The amount of wax necessaryto provide a fiber friction that results in such a level of resistiveforce can be readily determined by one skilled in the art by making testsamples of ribbon assemblies having different concentrations of theselected wax in the inner primary coating. The amount of wax requiredshould be determined using complete ribbon structures because, asdiscussed hereinabove, the presence of the outer primary coating willhave an effect on the strippability of the inner primary coating.

Suitable amounts of wax can also be closely approximated by using thefiber pull-out friction and crack propagation test methods describedherein, in which the amounts of wax that provide a predicted stripcleanliness of less than about 3 are preferred.

It has been found that suitable amounts of modified wax include fromabout 0.01% to about 10% by weight of the total inner primarycomposition, more preferably about 0.01% to about 5%, and mostpreferably about 0.01% to about 2%.

If desired, the wax can be further modified to include aradiation-curable functional group that can copolymerize withradiation-curable monomers and oligomers present in the inner primarycomposition. An example of such a radiation-curable functional wax isstearyl acrylate. The radiation-curable functional group in general doesnot have to be an acrylate group, but can be any known radiation-curablefunctional group, including those described herein.

The invention will be further explained by the following non-limitingexamples illustrating the use of waxes.

Examples 3-1 through 3-4

The components shown in Table 6 were combined to form four inner primarycoating compositions. Drawdowns of the inner primary coatingcompositions were made and then cured by exposure to UV light from aFusion D lamp, under a nitrogen atmosphere. The crack propagation andfiber friction for each of the films were tested in the same manner asabove, and the predicted strip cleanliness was calculated. The resultsare shown in Table 6.

TABLE 6 Example 3-1 Example 3-2 Example 3-3 Example 3-4 COMPONENT(Amount in % by weight of total composition) Linear Urethane Acrylate 23— — — Oligomer Having a Weight Average Molecular Weight of 5000,Urethane Acrylate Oligomer — 51.9 42.3 42.3 H-I-PTGL2000-I-PTGL2000-I-HLauryl Acrylate — 16 — — Ethoxylated Nonylphenol Acrylate 64.4 25.6 46.246.2 Glyceryl Propoxy Triacrylate 8 — — — Phenoxyethyl Acrylate — — 5 52,4,6,-Trimethyl 3 3 3 3 PhenylbenzoylDiphenyl Phosphine OxideThiodiethylene bis (3,5-di-tert- .5 0.5 0.5 0.5 butyl-4-hydroxy)hydrocinnamate Polyethylene/maleic anhydride .1 — — — copolymer wax(ceramer 1608) Methyl di (hydrogenated tallow) — 2 — — Amine IsocetylStearate — — 2 — PPG₁₂PEG₅₀ Lanolin — — — 2 Mercaptopropyl TrimethoxySilane 1 1 1 1 Test results Clarity Clear Clear Clear Clear Viscosity(mPa.s, 25 C.) 7650 6760 7390 Fiber Friction (g/mm) 7.7 11.4 7.2 CrackPropagation (mm) 1.53 1.56 1.69 Predicted Strip Cleanliness 2.1 2.5 1.9Fiber Pull-out Residue Test 2.3 The oligomers were formed by reactingthe following components: H = Hydroxyethyl Acrylate I = IsophoroneDiisocyanate PTGL2000 = 2000 molecular weightpolymethyltetrahydrofurfuryl/polytetrahydrofurfuryl copolymer diol(Mitsui, NY), the methyl group provides branching which reduces theorientation of the polymers formed from the oligomer

The fiber pull-out residue test was the same test as used previouslyexcept that the evaluation was quantified on a scale of 0 to 10, where 0is the best (no visible residue under 10×magnification) and 10 is theworst (lots of visible residue without use of magnification).

The test results in Table 6 demonstrate that modified waxes can be usedto adjust the fiber friction to a level that provides a resistive forceless than the cohesive strength of the inner primary coating, which isshown by the excellent predicted strip cleanliness values of less thanabout 3.

Radiation-curable, Silicone Containing Oligomers and Use ofNon-radiation-curable Silicone Compounds

Radiation-curable, silicone containing monomers and oligomers can alsobe used to adjust the level of fiber friction and thereby improve ribbonstrippability of the inner primary coating. The radiation-curable,silicone oligomer comprises a silicone compound to which at least oneradiation-curable functional group is bound. Preferably, two or moreradiation-curable functional groups are connected to the siliconeentity.

Preferably the radiation-curable functional group is capable ofcopolymerizing with the radiation-curable monomers and oligomers presentin the inner primary composition when exposed to suitable radiation.Therefore, the selection of the functional group will depend on themonomer or oligomer present in the inner primary composition. Oneskilled in the art will readily be able to determine which functionalgroups will cross-link with the monomer or oligomer present in the innerprimary composition. While not being limited thereto, examples ofsuitable functional groups are groups containing vinyl, acrylate,methacrylate, maleate, vinyl ether, or acrylamides, as well as thosedescribed herein above.

Examples of commercially available silicone compounds containing aradiation-curable functional group are silicone acrylates Ebecryl 350and Ebecryl 1360 (Radcure Industries), Tego Rad 2100, 2200, 2500, and2600 (Tego Chemie), and Coat-O-Sil 3503 (OSI Specialties).

Alternatively, based on the teachings herein, one skilled in the artwill be able to modify known silicone compounds to include the requiredradiation-curable functionality. For example, a silicone compoundprovided with hydroxy functionality can be reacted with a diisocyanatecompound and a compound containing a hydroxy and a radiation-curablefunctionality to provide a radiation-curable functionality to saidsilicone compound. Specific examples include reacting a siliconecompound containing a hydroxy functionality with a diisocyanate andhydroxyethylacrylate to provide an acrylate functionality on thesilicone compound, or isocyanate and hydroxybutylvinylether to provide avinyl ether functionality on the silicone compound. Example of suitablesilicone compound containing hydroxyl functionality include:polydimethylsiloxane diol of 1200 equivalent weight Q4-3667, DC 193 andDC 1248 (Dow Corning), HSi2111 (Tego Chemie), and Coat-O-Sil 3500 and3505 (Osi Specialties).

Alternatively, non-radiation-curable silicone compounds (hereinafterreferred to as “non-reactive silicone”) can be used to adjust the fiberfriction and thereby improve ribbon strippability of the inner primarycoating.

U.S. Pat. No. 4,496,210, which is incorporated herein by reference,discloses examples of suitable non-reactive silicones that can be used.Non-reactive silicones can be used separately or in conjunction with theradiation-curable silicone oligomers described herein.

The radiation-curable silicone oligomer and/or non-reactive siliconeshould be present in an amount to provide a fiber friction that resultsin a resistive force that is less than the cohesive strength of theinner primary composition. The amount of radiation-curable siliconeoligomer and/or non-reactive silicone is preferably the minimum amountrequired to provide a fiber friction that results in a resistive forceless than the cohesive strength of the inner primary composition. Suchminimum amount can easily be determined by making test runs of innerprimary compositions in which the amount of radiation-curable siliconeoligomers and/or non-reactive silicones present is varied. The lowestamount of radiation-curable silicone oligomers and/or non-reactivesilicones present which provides a fiber friction that results in aresistive force that is less than the cohesive strength of the innerprimary coating is the preferred amount.

A long chain silicone compound containing on average about oneradiation-curable functional group (monofunctional) bound near aterminus of the silicone compound can provide further advantages. Theend of the long silicone chain furthest from the radiation-curablefunctional group can be mechanically bound in the inner primary coating.However, upon heating during ribbon stripping, it is believed that theend of the long silicone chain farthest from the radiation-curablefunctional group can become unbound and diffuse toward the optical glassfiber/inner primary coating interface which is in the direction the heatis propagating. This diffusion of silicone increases at the criticalmoment during ribbon stripping to facilitate the clean removal of theentire coating system. The silicone acts as a lubricant between thesurface of the optical glass fiber and the inner primary coating.

The thickness of an inner primary coating usually varies from about 10microns to about 35 microns. Thus, a mono-functionalized silicone fluidhaving a molecular chain length of about 50,000 to about 350,000 Daltonscan diffuse toward the glass/inner primary coating interface duringribbon stripping.

Suitable amounts of radiation-curable silicone oligomers and/ornon-reactive silicones can also be closely approximated by using thefriction and crack propagation test methods described herein, in whichthe amounts of radiation-curable silicone oligomers and/or non-reactivesilicones that provide a predicted strip cleanliness of less than about3 are preferred.

The amount of radiation-curable silicone oligomer and/or non-reactivesilicones will also depend on the selection of the inner primarycomposition, in particular the initial fiber friction of the selectedinner primary coating composition. Generally, the higher the initialfiber friction (no slip additive), the greater the amount ofradiation-curable silicone oligomer and/or non-reactive silicone thatwill be required to lower the fiber friction to a level that provides aresistive force lower than the cohesive strength of the inner primarycoating.

In general, the radiation-curable silicone oligomers can be used ingreater amounts than non-reactive silicones because it is believed thatthe radiation-curable silicone oligomer will become bound in the innerprimary coating during curing, whereas the non-reactive silicone is freeto migrate throughout the cured inner primary coating. Alternatively,the radiation-curable silicone oligomer can be the main oligomer usedfor forming the inner primary coating. It has been found that suitableamounts of radiation-curable silicone oligomer are between about 0.1 toabout 90% by weight, preferably about 0.1 to about 60% by weight, andmore preferably about 0.1 to about 30% by weight. In general, highermolecular weight radiation-curable silicone oligomers will be present ina radiation-curable coating in greater weight percentages than lowermolecular weight composite oligomers.

Suitable amounts of mono-functionalized monomers have been found to beabout 0.1 to about 20% by weight, more preferably about 0.1 to about 10%by weight, and most preferably about 0.1 to about 5%.by weight.

Suitable amounts of non-reactive silicone are between about 0.01 toabout 10% by weight, preferably about 0.01 to about 5% by weight, andmore preferably about 0.01 to about 1% by weight.

The invention will be further explained by the following non-limitingexamples illustrating the use of silicone entities.

EXAMPLE 4-1

The components shown in Table 7 were combined to form an inner primarycoating composition. A film of the coating material (75 micron thick)was prepared on glass slides and then cured by exposure to UV light inthe same manner as above. The tensile strength, elongation and moduluswere measured.

A 75 micron film of the coating material was also prepared and suitablycured. The crack propagation was then measured. A friction test was alsoconducted, as described herein. The predicted ribbon strip cleanlinesswas calculated. The results are shown in Table 7.

TABLE 7 Example 4-1 Component (Amount is % by weight of totalcomposition) Oligomer H-DesW-PTHF2900-DesW-H 47.5 EthoxylatedNonylphenol Acrylate 29 Lauryl Acrylate 14.2 2,4.6-TrimethylPhenylbenzoyl Diphenyl 3 Phosphine Oxide Silicone Oligomer 5H-I-HSi2111-I-H y-Mercaptopropyltrimethoxy Silane .8 Thiodiethylene Bis(3,5-di-tert-Butyl-4- .5 Hydoxy) Hydocinnamate Test Results Viscosity,mPa.s (25 C.) 6040 Tensile Strength, Mpa 1 Elongation, % 140 Modulus,Mpa 1.4 Dose at 95%, Modulus, J/Sq CM .38 Crack Propagation (mm) 1.7Fiber Pull-Out Friction (g/mm) 17.1 Predicted Strip Cleanliness 2.5-3The oligomers were formed by reacting the following components: H =Hydroxyethyl Acrylate DesW = bis 4,4-(isocyanatocyclohexyl)methane I =Isophorone Diisocyanate PTHF2900 = 2900 molecular weightPolytetramethylene Ether (BASF) HSi2111 = a silicone diol having a MW of1000 (Tego Chemie)

EXAMPLES 4-2 THROUGH 4-10

The components shown in Table 8 were combined to form 11 different innerprimary coating compositions. The viscosity and clarity of thecompositions was determined.

Films of the coating materials (75 micron thick) were prepared onmicroscope slides and then cured by exposure to UV light in the samemanner as above. The tensile strength, elongation and modulus weremeasured.

Additional films of the coating materials were also prepared andsuitably cured. The crack propagation was then measured. A friction testwas also conducted, as described herein. The predicted ribbon stripcleanliness was calculated. The results are shown in Table 8.

TABLE 8 Ex. Ex. Ex. Ex. Ex. Ex. Ex. Ex. Ex. 4-2 4-3 4-4 4-5 4-6 4-7 4-84-9 4-10 Component (Amount is % by weight of total composition) Oligomer45.67 H-I-PTHFCD2000-I- PTHFCD2000-I-H Oligomer 54.86 H-(I-PPG1025)1.06-(- PERM) 1.14-I-H Oligomer 60.65 H-I-PTGL2000-I-H Oligomer 67.5 70H-I-PTG2010-I-PPG2010-I-H Oligomer 51.02 49.23 43H-I-PTGL2000-I-PTGL2000-I-H Oligomer 78 (H-I)₃-TPE4542 EthoxylatedNonylphenol 34.48 24.99 32.85 20.14 24.75 16 50.5 Acrylate Ester LaurylAcrylate 14.35 13.72 6.92 16.64 Isodecyl Acrylate Phenoxyethyl Acrylate16.62 2.5 Mole Propoxylated Nonyl 25.00 23.5 Phenol Acrylate 25:75weight/weight of 2.94 3 Bis (2,6- Dimethoxybenzoyl) (2,4,4-Trimethylpentyl) Phosphine Oxide and 2-Hydroxy-2- Methyl-1-PhenylPropanone 2,4,6-trimethylbenzoyl 3 2.5 3 3 1 3 Diphenyl Phosphine Oxide1-Hydroxycyclohexyl Phenyl 4 2 Ketone Octadecyl 3,5-Bis (1,1- .5 .5Dimethylethyl)-4- Hyroxybenzenepropanone Thiodiethylene bis (3,5-di- .49.5 .3 .5 Tert-Butyl-4- Hydroxy) hydrocinnamateDitridecylthiodipropionate 1 1 Free Silicone, DC-193 (Dow 1 2 1 2 2Corning) Free Silicone, DC-190 (Dow 1 Corning) Teograd 2100 silicone 2.51 5 acrylate L-77 Polyethylene oxide modified Dimethylsiloxane1-Propanethiol,3- 1 1 .98 1 1 1 .92 1 1 (Trimethoxysilyl) Clarity WhenMade clear clear clear clear clear Clarity After 24 Hours at 4 clearclear clear C. Clarity After 24 Hours at clear clear clear −20 C.Clarity After 3 Days at 60 clear clear clear C. Viscosity (mPa · s, 25C.) 8700 5600 8000 9520 7170 6240 8200 Dose @ 95% Modulus .77 .46 .45.32 .36 .45 .2 (J/sq. cm) Tensile Strength (MPa) .4 1.5 .6 1.1Elongation (%) 50 100 140 180 Modulus (Mpa) 1.2 2.7 1.1 1.3 2.4 FiberFriction (g/mm) 3.1 4.9 2.7 4.4 21 18.4 18.5 3 3.4 Fiber Friction (g/mm)After 1 1.4 7 days, 60 C., dose 95% of dose required for complete cureCrack Propagation (mm) 2.1 1.49 1 1.4 1.21 1.82 1.47 1.1 1.9 Crackpropagation (mm) 1.1 after 7 days, 60 C., dose 95 of dose required forcomplete cure Predicted Strip Cleanliness 1.5-2 1.5 2.2 1.5 3.6 3 3 1.51.5 The oligomers were formed by reacting the following components: H =Hydroxyethyl Acrylate I = Isophorone Diisocyanate PTHFCD2000 = isPolyTHF containing some carbonate linkages PPG1025 = isPolypropyleneoxidediol having an average molecular weight of 1000 (Arco)PPG2010 = is Polypropyleneoxidediol having an average molucular weightof 2000 (BASF) PTGL2000 = 2000 molecular weightpolymethyltetrahydrofurfuryl/polytetrahydrofurfuryl copolymer diol(Mitusi, NY) TPE4542 = polypropylene glycol ethylene oxide endcappedtriol (BASF) Perm = Permanol KM10-1733 polycarbonate/polyether copolymerdiol

The test results in Table 8 demonstrate that the radiation-curablesilicone oligomers and non-reactive silicones can be used to adjust thefiber friction to a level that provides a resistive force less than thecohesive strength of the inner primary coating, which is shown by thepredicted strip cleanliness values of about 3 or less.

Radiation-curable Fluorinated Oligomers and Fluorinated Materials

The fiber friction between the inner primary coating and the surface ofthe optical glass fiber can also be significantly reduced byincorporating radiation-curable fluorinated oligomers, monomers and/ornon-radiation curable fluorinated materials into the inner primarycoating composition. The radiation-curable, fluorinated oligomer ormonomer comprises a fluorinated compound to which at least oneradiation-curable functional group is bound. Preferably, two or moreradiation-curable functional groups are connected to the fluorinatedentity.

Preferably the radiation-curable functional group is capable ofcopolymerizing with the radiation-curable monomers and oligomers presentin the inner primary composition when exposed to suitable radiation.Therefore, the selection of the functional group will depend on themonomer or oligomer present in the inner primary composition. Oneskilled in the art will easily be able to determine which functionalgroups will cross-link with the monomer or oligomer present in the innerprimary composition. While not being limited thereto, examples ofsuitable radiation-curable functional groups are groups containingvinyl, acrylate, methacrylate, maleate, vinyl ether, or acrylamides, aswell as those described herein above.

Examples of commercially available fluorinated compounds containing atleast one radiation-curable functional group include

perfluoro ethyl acrylate (DuPont), 2-(N-Ethylperfluoro OctaneSulfonamido) Ethyl Acrylate (3M), 1H, 1H-pentadecafluoroctyl acrylate(Oakwood Research Chemicals), as well as methacrylate or N butylacrylate versions of these.

Based on the teachings herein, one skilled in the art will be able tomodify a fluorinated compound to include the required radiation-curablefunctionality. For example, a fluorinated compound provided with hydroxyfunctionality can be reacted with a diisocyanate compound and a compoundcontaining a hydroxy and a radiation-curable functionality to provide aradiation-curable functionality to said fluorinated compound. Specificexamples include reacting a fluorinated compound containing a hydroxyfunctionality with a diisocyanate and hydroxyethylacrylate to provide anacrylate functionality on the fluorinated compound, or isocyanate andhydroxybutylvinylether to provide a vinyl ether functionality on thefluorinated compound. Examples of suitable fluorinated compoundscontaining hydroxyl functionality include Fluorolink E (Ausimont),2-methyl-4,4,4-trifluorobutanol, 1H,1H-pentadecafluoro-1-octanol,1H,1H-pentafluoropropanol-1, and1H,1H,12H,12H-perfluoro-1,12-dodecanediol (Oakwood Research Chemicals).

Alternatively, non-radiation-curable fluorinated compounds (hereinafterreferred to simply as “fluorinated compounds”) can be used to adjust thefiber friction and thereby improve ribbon strippability of the innerprimary.

The fluorinated compounds can be used separately or in conjunction withthe radiation-curable silicone oligomers or monomers described herein.

The radiation-curable fluorinated oligomer or monomer and/or fluorinatedcompounds should be present in an amount to provide a fiber frictionthat results in a resistive force that is less than the cohesivestrength of the inner primary composition. The amount ofradiation-curable fluorinated oligomer and/or fluorinated compound ispreferably the minimum amount required to provide a fiber friction thatresults in a resistive force less than the cohesive strength of theinner primary composition. Such minimum amount can easily be determinedby making test runs of inner primary compositions in which the amount ofradiation-curable fluorinated oligomers or monomers and/or fluorinatedpresent is varied. The lowest amount of radiation-curable fluorinatedoligomers or monomers and/or fluorinated compounds present whichprovides a fiber friction that results in a resistive force less thanthe cohesive strength of the inner primary coating is the preferredamount.

Suitable amounts of radiation-curable fluorinated oligomers or monomersand/or fluorinated compounds can also be closely approximated by usingthe friction and crack propagation test methods described herein, inwhich the amounts of radiation-curable fluorinated oligomers or monomersand/or fluorinated compounds that provide a predicted strip cleanlinessof less than about 3 are preferred.

The amount of radiation-curable fluorinated oligomer or monomers and/orfluorinated compounds will also depend on the selection of the innerprimary composition, in particular the initial fiber friction of theselected inner primary coating composition. Generally, the higher theinitial fiber friction (no slip additive), the greater the amount ofradiation-curable fluorinated oligomer or monomer and/or fluorinatedcompounds that will be required to lower the fiber friction to a levelthat provides a resistive force lower than the cohesive strength of theinner primary coating.

In general, the radiation-curable fluorinated oligomers or monomers canbe used in greater amounts than non-reactive fluorinated compoundsbecause it is believed that the radiation-curable fluorinated oligomersor monomers will become bound in the inner primary coating duringcuring, whereas the non-reactive fluorinated compounds are free tomigrate throughout the cured inner primary coating. Alternatively, theradiation-curable fluorinated oligomer or monomer can be the mainoligomer used for forming the inner primary coating. It has been foundthat suitable amounts of radiation-curable fluorinated oligomer ormonomer are between about 0.1 to about 90% by weight, preferably about0.1 to about 60% by weight, and more preferably about 0.1 to about 30%by weight. In general, larger molecular weight oligomers can be used ingreater amounts than lower molecular weight oligomers or monomers.

Suitable amounts of fluorinated compounds have been found to be betweenabout 0.01 to about 10% by weight, preferably about 0.01 to about 5% byweight, and more preferably about 0.01 to about 1% by weight.

The invention will be further explained by the following non-limitingexamples illustrating the use of fluorinated materials.

EXAMPLES 5-1 THROUGH 5-3

The components shown in Table 9 were combined to form 5 different innerprimary coating compositions. The viscosity and clarity of thecompositions were determined.

Films of the coating materials (75 micron thick) were prepared on glassslides and then cured by exposure to UV light in the same manner asabove. The tensile strength, elongation and modulus were measured.

Additional films of the coating materials were also prepared andsuitably cured. The crack propagation was then measured. A friction testwas also conducted, as described herein. The predicted ribbon stripcleanliness was calculated. The results are shown in Table 9.

TABLE 9 Ex. Ex. Ex. 5-1 5-2 5-3 Component (% by weight based on totalcomposition) Oligomer 54.32 55.58 H-(I-PPG1025)_(1.06)-(-PERM)_(1.14)-I-H Oligomer H-(I-PPG2010)₂-I-H 67.75 EthoxylatedNonylphenol 24.74 25.31 Acrylate Ester Isodecyl Acrylate 13.58 13.9 2.5Mole Propoxylated Nonyl 25 Phenol Acrylate 25:75 weight/weight of 2.91 3Bis(2,6- Dimethoxybenzoyl) (2,4,4- Trimethylpentyl) Phosphine Oxide and2-Hydroxy-2-Methyl- 1 -Phenyl Propanone 1-Hydroxycyclohexyl Phenyl 4Ketone - Octadecyl 3,5-Bis(1,1- 0.50 Dimethylethyl) -4-HyroxybenzeneprOpanofle Thiodiethylene bis(3,5-di- .48 .5 tert-butyl-4-hydroxy) Hydrocinnainate Ditridecyithiodipropicnate 1.00 Foralkyl EM-63.00 Tridecafluorooctyl Mecaptan (Elf Autochem) Fluorosulfonamide (3M)0.75 .75 mercaptopropyl trimethoxy 0.97 1 1 silane Clarity as made ClearClear Clear Clarity after 24 hours at 4° C. Clear Clarity after 24 hoursat - Clear 20° C. Clarity after 3 days at 60° C. Very Few Incom pat'sViscosity (mPa.s, 25 C.) 6200 Dose @ 95% Modulus (J/sq.cm) .77 0.50 .47Tensile Strength (MPa) 0.50 Elongation (%) 88 Modulus (MPa) 1.20 FiberFriction (g/mm) 25.5 8.2 10.5 Fiber Friction (g/mm) After 7 1.1 days, 60C., at dose of 95% of dose for complete cure Crack Propagation (mm) 1.321.54 1.1 Crack Propagation (mm) after 7 1 days, 60 C., at dose of 95% ofdose for complete cure Predicted Strip Cleanliness 3.0 2.0 2.6 TableNotes: The oligomers were formed by reacting the following components: H= Hydroxyethyl Acrylate; I = Isophorone Diisocyanate PP1025 = isPolypropyleneoxidediol having an average molecular weight of 1000 (Arco)PPG2010 = is Polypropylenediol having an average molecular weight of2000 (BASF) PTGL2000 = 2000 molecular weightpolymethyltetrahydrofurfuryl/polytetrahydrofurfuryl copolymer diol(Mitsui, NY) Perm = Permanol KM10-l733 polycarbonate/polyether copolymerdiol

Solid Lubricants

Surprisingly, it has been found that solid lubricants can be added tothe inner primary composition to reduce the fiber friction between theinner primary coating and the surface of the optical glass fiber. Theterm “solid lubricant” is used herein to mean that the lubricant issubstantially insoluble in the inner primary composition and that theparticle or flake shape of the solid lubricant is substantiallymaintained after curing of the inner primary coating composition.

Usually the solid lubricant is non-reactive with the components of innerprimary coating composition. Examples of suitable non-reactive solidlubricants are the following, but not limited thereto:

solid organic lubricants including organic polysaccarides such as sodiumalginate, polyolefins, polyvinyl alcohol, nylon such as Orgasol (ElfAtochem), solid Teflon particles, and hard waxes such as Rad Wax; solidinorganic lubricants including molybdenum disulfide, graphite, silicatessuch as talc, clays such as kaolin and mica, silica, and boron nitride.

However, if desired, a reactive solid lubricant can be used. Reactivesolid lubricants contain a radiation-curable functional group.Preferably, the radiation-curable functional group is capable ofcopolymerizing with the radiation-curable monomers or oligomers presentin the inner primary composition. The radiation-curable functional groupcan be, for example, any of the radiation-curable functional groupsdescribed herein. Specific examples of suitable reactive solidlubricants include zinc acrylate, molybdenum acrylate, aluminumacrylate, barium acrylate, and chromium acrylate.

The particle size is preferably small enough to avoid microbendingcaused by the solid particles exerting stresses on the surface of theoptical glass fiber during use. Furthermore, the particle size ispreferably small enough to avoid causing the inner primary coating to behazy in appearance. Examples of suitable particle sizes have been foundto be about 10 microns or less, preferably about 5 microns or less, andmost preferably less than about 2 microns.

Alternatively to the particle size, the hardness of the solid lubricantis preferably low enough to avoid microbending caused by the solidparticles exerting stresses on the surface of the optical glass fiberduring use. In general, a softer solid lubricant will be less likely tocause such microbending.

Based on the teachings provided herein, one skilled in the art willeasily be able to use the selected solid lubricant in an amount toprovide the desired level of fiber friction between the inner primarycoating and the surface of the optical glass fiber. The amount of thesolid lubricant present in the inner primary composition will depend onthe ability of the solid lubricant to impart the desired reduction inthe fiber friction between the inner primary coating and the surface ofthe optical glass fiber, and the amount the fiber friction must bereduced to provide a fiber friction level that results in a resistiveforce less than the cohesive strength of the inner primary coating. Ingeneral, the greater the ability of the solid lubricant to reduce fiberfriction, the less solid lubricant that will be required. Preferably,the amount of solid lubricant present is about the minimum amountnecessary to provide a level of fiber friction necessary to provide aclean, residue free optical glass fiber after ribbon stripping. Asdiscussed above, the fiber friction level that will provide a clean,optical glass fiber after ribbon stripping will depend on the cohesivestrength of the inner primary coating. The greater the cohesive strengthof the inner primary coating, the greater the amount of fiber friction,and resulting resistive force, that can be tolerated and still provide aclean, bare optical glass fiber after ribbon stripping. The amount ofsolid lubricant necessary to provide such a level of fiber friction canbe easily determined by one skilled in the art by making test samples ofribbon assemblies having different concentrations of the selected solidlubricant in the inner primary coating. The amount of solid lubricantrequired should be determined using complete ribbon structures because,as discuss herein above, the presence of the outer primary coating willhave an effect on the strippability of the inner primary coating.

Suitable amounts of solid lubricant can also be closely approximated byusing the fiber pull-out friction and crack propagation test methodsdescribed herein, in which the amounts of solid lubricant that providesa predicted strip cleanliness of less than about 3 are preferred.

It has been found that suitable amounts of solid lubricant include fromabout 0.1% to about 20% by weight of the total inner primarycomposition, more preferably about 0.1% to about 10%, and mostpreferably about 0.1% to about 5%.

Preferably, a surfactant is used in combination with the solidlubricant. Examples of a suitable surfactants include: fluorosulfonamidesurfactant (3M), 3,6-dimethyl-4-octyne-3,6-diol (Air Products), linearcopolymer of vinylpyrolidone and long chain alpha olefin (InternationalSpecialty Products), Solsperse high MW polymeric dispersing agents(Zeneca), and other well-known anionic, cationic and non-ionicsurfactants.

The invention will be further explained by the following non-limitingexamples.

EXAMPLES 6-1 THROUGH 6-3

The components shown in Table 10 were combined to form 8 different innerprimary coating compositions. The viscosity and clarity of thecompositions was determined.

Films of the coating materials (3 mil) were prepared on microscopeslides and then cured by exposure to UV light in the same manner asabove. The tensile strength, elongation and modulus were measured.

75 mm films of the coating materials were also prepared and suitablycured. The crack propagation was then measured. A fiber pull-outfriction test was also conducted, as described herein. The predictedribbon strip cleanliness was calculated. The results are shown in Table10.

TABLE 10 Ex. Ex. Ex. 6-1 6-2 6-3 Component (Amount is % by weight oftotal composition) Oligomer H-(I-PTGL2000)₂-I-H 36.1 42.3 36.1Ethoxylated Nonylphenol Acrylate 44.4 46.1 43.9 Phenoxyethyl Acrylate 55 5 2,4,6-trimethylbenzoyl Diphenyl 3 3 3 Phosphine Oxide and2-Hydoxy-2- Methyl-1-Phenyl-1-Propanone blend Thioethylenebis(3,5-di-tert- .5 .5 .5 butyl-4-Hydroxy) Hydrocinnamatey-Mercaptopropyltrimethoxy 1 1 1 Silane Rad Wax 62EB (33% PE wax in 10epoxy acrylate) Fluorosulfonamide Surfactant FC- .1 .5 430 (3M) Fluoro A(Micronized PTFE) 2 10 Test results Clarity (opaque?) yes yes yes Colorwhite white white Viscosity, mPa.s at 25° 5440 7960 7520 Film Opacity, 3mil opaque cloudy cloudy Fiber Friction (g/mm) 15.2 8.2 6.6 CrackPropagation (mm) 1.96 2.2 Predicted Strip Cleanliness 2.2 2.4 Theoligomers were formed by reacting the following components: H =Hydroxyethyl Acrylate I = Isophorone Diisocyanate PTGL2000 = 2000molecular weight polymethyltetrahydrofurfuryl/polytetrahydrofurfurylcopolymer diol (Mitsui, NY) Perm = Permanol KM10-1733polycarbonate/polyether copolymer diol

The test results in Table 10 demonstrate that solid lubricants can beused to reduce the friction to a level that results in a resistive forceless than the cohesive strength of the inner primary coating, which isshown by the predicted strip cleanliness values of about 3 or less.

Use of Novel Slip Agents

The above described novel slip agents can be used alone, in combinationsof novel slip agents, as novel slip agents with conventional slipagents, and as novel slip agents in combination with the adjusting thenormal force as desired to provide the desired level of fiber friction.

Based on the above experimental data, the composition of the innerprimary coating can surprisingly be formulated or selected to provide afiber friction of about 40 (g/mm) or less, preferably about 30 (g/mm) orless, and more preferably about 20 (g/mm), and most preferably about 10(g/mm) or less at the desired ribbon stripping temperature, incombination with a crack propagation of the inner primary coating whichis greater than about 0.7 mm, preferably greater than about 1 mm, morepreferably greater than about 1.5 mm, and most preferably greater thanabout 2 mm, at the desired/design ribbon stripping temperature, such as90° C. Table 11 and example 11-1 illustrates a practice according tothis invention.

TABLE 11 Example 11-1 Component (% weight based on total weight ofcomposition) Oligomer H-(I-PTGL2000)₂-I-H 50.3 Isobornyl Acrylate 10Ethoxylated Nonylphenol Acrylate Ester 15.1 Thiodiethylene bis(3,5-di-tert-butyl-4-Hydroxy) 0.5 Hydrocinnamate Phenoxy Ethyl Acrylate20 2,4,6-Trimethylbenzoyl Diphenyl Phosphine Oxide 3 Silicone Fluid¹ 0.1gamma-Mercaptopropyl Trimethoxy Silane 1 Test Results Predicted StripCleanliness 2.5 Fiber Friction (g/mm) 18.5 Crack Propagation (mm) 2.07The oligomers and monomers were formulated from the followingcomponents: H = Hydroxyethylacrylate I = IsophoronediisocyanatePTGL2,000 = polymethyltetrahydrofurfuryl/polytetrahydrofurfurylcopolymer diol having the molecular weight (2,000), (Mitsui, NY)Silicone Fluid = Byk333 (BYK Chemie) which is polydimethylsiloxane withterminal polyethylene oxide groups

Linear Oligomers

If desired, ribbon strippability can also be improved by increasing theability of the inner primary coating to transmit force applied duringribbon stripping. In general, the more efficient the inner primarycoating is at transmitting the force applied during the ribbon strippingoperation, the less stripping force that need be applied to remove theinner primary coating.

It has now also been found that the use of linear oligomers can improvethe effectiveness, and consequently the efficiency, of the inner primarycoating to transmit the ribbon stripping forces applied during ribbonstripping operations. In general, to the extent that the molecularstructure of the oligomer is designed to be more linear, the moredensely the oligomers will pack together when forming the inner primarycoating. It has been found that as the oligomers become more denselypacked, the more efficiently the inner primary coating can transmit thestripping force applied during ribbon stripping.

The ability of a ribbon assembly to strip cleanly during ribbonstripping can be further improved if the polymers bound in the outerprimary coating have the ability to orient upon heating.

Examples of linear, radiation-curable oligomers according to the presentinvention that provide enhanced strippability can be illustrated by thefollowing formula (4):

R¹—L—[R²—L]_(n)—R³  (4)

wherein: R¹ and R³ are organic groupings having radiation-curablefunctional groups as defined herein, and R² is an optional organicradical;

L is a linking group, providing a bridging group such as a urethane,thio-urethane, urea or ester grouping, as defined herein, preferablyurethane;

R² is a substantially linear carbon-containing entity; and n is about 1to about 40, preferably about 1 to about 20, and most preferably about 1to about 10, wherein the molecular weight of [R²—L]_(n) is about 500 toabout 20,000, preferably about 1,000 to about 10,000, and mostpreferably about 1,500 to about 6,000.

When n is 1, [R²—L] can contain, for example, a polyolefin, polyether,polycarbonate, or polyester structure having a molecular weight of about500 to about 20,000. When n is from about 2 to about 5, [R²—L] caninclude a polyolefin, polyether, polycarbonate, or polyester having amolecular weight of about 500 to about 10,000. When n is from about 5 toabout 30, [R²—L] can represent a polyolefin, polyether, polycarbonate,or polyester having a molecular weight of about 500 to about 4,000.

The linear oligomers according to this invention can be used in anamount suitable to provide the desired level of ribbon strippingperformance. The desired amount can easily be found and determined byone skilled in the art by testing different amounts of the selectedlinear oligomer(s) in an inner primary coating, and optionally in anouter primary coating as well, on optical glass fibers encased in aribbon assembly. It has generally been found that the linear oligomersaccording to this invention can be used in amounts of about 0.1 to about90 wt. %, preferably about 5 to about 80 wt. %, more preferably about 5to about 60 wt. %, based on the total weight of the inner primary orouter primary composition.

EXAMPLE 7-1 THROUGH 7-2

The components shown in Table 12 were combined to form an inner primarycoating composition. The compositions were cured and the fiber pull-outfriction of the cured coating was measured, as defined herein. The testresults are shown in Table 12.

TABLE 12 Example Example 7-1 7-2 Component (Amount is % by weight oftotal composition) Oligomer H-(I-PTHF2000)₂-I-H 52.26 52.26 EthoxylatedNonylphenol Acrylate 15.7 15.67 Lauryl Acrylate 15.19 16.19 n-VinylFormamide Isobornyl Acrylate 11.8 0 n-Vinyl Formamide EthylhexylAcrylate 0 10.8 25:75 weight/weight of Bis(2,6-Dimethoxy- 3.7 3.7benzoyl) (2,4,4-Trimethylpentyl) Phosphine Oxide and2-Hydroxy-2-Methyl-1-Phenyl Propanone gamma-Mercaptopropyl TrimethyoxySilane 0.92 0.92 Thioethylene Bis(3,5 di-tert-butyl-4-hydroxyl) .46 .46Hydrocinnamate (antioxidant) Test Results Fiber Pull-Out Residue Test0.875 1.25 The oligomer was formed by reacting the following components:H = Hydroxyethyl Acrylate I = Isophorone Diisocyanate PTHF2000 = 2000molecular weight Polytetramethylene Ether Glycol (BASF)

Terminal Linear Moieties

It has been found that the use of radiation-curable oligomers containingat least one terminal linear moiety can also improve the efficiency ofthe inner primary coating to transmit the stripping force applied duringthe ribbon stripping operation.

Examples of radiation-curable oligomers according to the presentinvention that provide enhanced strippability can be illustrated by thefollowing formula:

R⁴—x—L—x—[R⁵—x—L—x]_(n)—R⁶

wherein

R⁴ is a substantially linear long chain alkyl terminating in at leastone hydroxyl group;

each L represents, independently, a molecular bridging group, preferablyderived from a diisocyanate precourser reactant;

each x represents a resulting reacted linking group, such as, interalia, a urethane, thio-urethane, or urea entity.

Alternatively, ester linkages can also be utilized;

R⁵ is a linear or a branched or cyclic hydrocarbon or polyether moietyderived from a a diol and having a molecular weight of from 150 to10,000, preferably from 500 to 5,000, and most preferably from 1,000 to2,000 Daltons;

R⁶ is an end group carrying a radiation-curable functional group asdefined herein, preferably an acrylate or methacrylate; and also havingan hydroxyl linkage to the L entity.

R⁴ preferably has at least about 80%, more preferably at least about90%, of its carbon atoms in a straight chain; and,

n may represent a number from zero to 30.

Preferably, R⁴ is an alkyl radical with of from about C₉ to about C₂₀,since longer carbon chains may decrease the resistance against oil.Suitable examples of alkyls are lauryl, decyl, isodecyl, tridecyl, andstearyl. Most preferred is lauryl.

R⁵ can contain a branched or cyclic aliphatic group having about 6 toabout 15 carbon atoms. In particular R⁵ can be the aliphatic componentof a diisocyanate compound such as isophorone diisocyanate, DesW, TMDI,and HXDI. If R⁵ is a branched component, preferably, the extent ofbranching units is at least about 10 mole %, and more preferably atleast about 20 mole %, based on the total number of carbon atoms in R⁵.

The oligomers according to above formula can be made, for example, byreacting in a first reaction one mole of a diisocyanate compound (forforming R⁵⁾ with (1) one mole of a long chain alkyl containing a hydroxygroup (for forming R⁴)or (2) one mole of a compound containing a hydroxyfunctional group and a radiation-curable functional group (for formingR⁶). The urethane linking group “x” attached to “L” is formed by thereaction of the isocyanate group with a hydroxyl group. In a secondreaction, the remaining isocyanate group is reacted with the other asyet unreacted hydroxyl group of the compound. Reactions of hydroxyfunctional compounds with isocyanate functional molecules are well knownin the art, and can be catalyzed if needed, with known catalysts.Suitable examples of reactants containing a radiation-curable functionalgroup and a hydroxy group are hydroxyethylacrylate or2-hydroxypropylacrylate. Suitable examples of linear long chain alkylsinclude lauryl alcohol, decyl alcohol, isodecyl alcohol, tridecylalcohol, and stearyl alcohol.

The resulting radiation-curable oligomer can be used in optical glassfiber coatings, in particular in inner primary coatings, as a monomerthat enhances the strippability of the final coating, and that yields acoating composition which may have a high cure speed.

The radiation-curable oligomers according to this invention canaccordingly be used in amounts suitable to provide the desired level ofribbon stripping performance. The desired amount can easily bedetermined by one skilled in the art by simple testing of differentamounts of the selected linear oligomer(s) in an inner primary coating,and optionally in an outer primary coating as well, on optical glassfibers encased in a ribbon assembly. It has been found that theoligomers provided by this invention can generally be used in amounts ofabout 1 to about 90 wt. %, preferably about 5 to about 80 wt. %, andmost preferably about 5 to about 60 based on the total weight of theinner primary or outer primary composition.

EXAMPLE 8-1 Comparative Examples H-1 through H-3

The components shown in Table 13 were combined to inner primary coatingcompositions.

75 micron thick films of the coating materials were prepared andsuitably cured. The fiber pull-out friction test was conducted, asdescribed herein, and the test results are shown in Table 13.

TABLE 13 Comp. Comp. Comp. Example Example Example Example H-1 H-2 H-38-1 Component (Amount is % by weight of total composition) Oligomer H-52.26 52.26 52.56 52.56 (I-PTHF2000)₂-I-H Ethoxylated Nonylphenol 15.6715.67 15.67 15.67 Acrylate Lauryl Acrylate 3.39 10.79 10.79 7.15 n-VinylFormamide 23.6 0 0 0 Isobornyl Acrylate n-Vinyl Formamide 0 16.2 21.6 0Ethylhexyl Acrylate n-Vinyl Formamide 0 0 0 19.84 Butyl Acrylate 25:75weight/weight of 3.7 3.7 3.7 3.7 Bis(2,6-Dimethoxy- benzoyl) (2,4,4-Tri-methylpentyl) Phosphine Oxide and 2-Hydroxy-2- Methyl-1-Phenyl Propanonegamma-Mercaptopropyl 0.92 0.92 0.92 0.92 Trimethyoxy Silane ThioethyleneBis(3,5 di- 0.46 0.46 0.46 0.46 tert-butyl-4-hydroxyl) Hydrocinnamate(antioxidant) Test Results Fiber Pull-Out 1.5 0.75 1 0.65 Residue TestThe oligomer was formed by reacting the following components: H =Hydroxyethyl Acrylate I = Isophorone Diisocyanate PTHF2000 = 2000molecular weight Polytetramethylene Ether Glycol (BASF)

The test results in Table 13 demonstrate that as the length of thelinear moiety is increased, the fiber pull-out friction decreases.

Aromatic Groups

Ribbon strippability can also be enhanced by incorporating a highconcentration of aromatic groups in the oligomers and monomers used toform the inner primary coating. It will be appreciated that coatingcompositions comprising about 0.1 or more moles of aromatic groups per100 grams of total composition, calculated using the molecular weightsof the compositional components, are regarded as having a highconcentration of aromatic groups. It is believed that the planarity ofthe phenyl ring next to the surface of the optical glass fiber may allowfor the good slidability of the inner primary coating off the opticalglass fiber during ribbon stripping.

EXAMPLE 9-1

The components shown in Table 14 were combined to form an inner primarycoating composition.

A 75 micron thick film of the coating material was prepared and suitablycured. The crack propagation was then measured. A friction test was alsoconducted, as described herein. The results are shown in Table 14.

TABLE 14 Example 9-1 Component (Amount is % by weight of totalcomposition) Oligomer H-I-(PTGL2000-I)₂-H 51.54 Ethoxylated NonylphenolAcrylate 20.86 Phenoxyethyl Acrylate 16.8 Lauryl Acrylate 7 25:75weight/weight of Bis(2,6-Dimethoxybenzoyl) 2.5 (2,4,4-Trimethylpentyl)Phosphine Oxide and 2-Hydroxy-2-Methyl-1-Phenyl Propanone ThiodiethyleneBis(3,5-di-tert-butyl-gamma- 0.3 hydroxy) Hydrocinnamategamma-Mercaptopropyl Trimethoxy Silane 1 Test Results Crack Propagation(mm) 1.49 Fiber Pull-Out Friction (g/mm) 10 Predicted Strip Cleanliness2 The oligomer was formed by reacting the following components: H =Hydroxyethyl Acrylate I = Isophorone Diisocyanate PTGL2000 = 2000molecular weight polymethyltetrahydrofurfuryl/polytetrahydrofurfurylcopolymer diol (Mitsui, NY)

High Molecular Weight Polymeric Blocks and Reduced Concentration ofUrethane

Radiation-curable, inner primary optical glass fiber coatingcompositions (hereinafter referred to as “inner primary compositions”)are now well known in the art. Such inner primary compositions usuallycontain at least one radiation-curable oligomer, and optionally reactivediluents, photoinitiators, and additives, as described herein above.

It has now been found that by reformulating the radiation-curableoligomer used in the inner primary composition, an inner primary coatingcan be formed having a significantly increased crack propagation incombination with a significantly decreased fiber friction. Furthermore,it has been found that the crack propagation can be increased and thefiber friction decreased to levels which provide the inner primarycoating with the ability to strip cleanly from the surface of an opticalglass fiber during ribbon stripping, without the use of substantialamounts of slip agents in the inner primary coating. In some instances,the use of slip agents can be substantially avoided. The term slipagents includes components which are separate and distinct from theradiation-curable oligomer as well as slip agent moieties that can bebound to the radiation-curable oligomer. The use of slip agents maycause undesirable delamination of the inner primary coating during useof the ribbon assembly in hot and wet environments, such as tropicalenvironments, which can lead to microbending and attenuation of thesignal transmission. Thus, by substantially avoiding the use of slipagents to provide a ribbon-strippable inner primary coating, the presentinvention can provide a ribbon-strippable inner primary coating whichexhibits enhanced resistance to such undesirable delamination.

Radiation-curable, oligomers comprising a carbon containing backbone towhich at least one radiation-curable functional group is bound are wellknown in the art. Usually, the carbon containing backbone of theradiation-curable oligomer contains one or more polymeric blocks eachhaving a molecular weight up to about 2000 and being connected togethervia coupling groups. Thus, an oligomer having a molecular weight ofabout 6000, will usually contain three polymeric blocks each having amolecular weight of about 2000 which are connected via coupling groups.The radiation-curable functional groups are also usually connected tothe carbon-containing backbone via coupling groups.

By extensive experimentation, it has now been found that as themolecular weight of the polymeric blocks is increased, the crackpropagation of the inner primary coating increases and the fiberfriction of the inner primary coating decreases. The molecular weight ofthe polymeric blocks should be adjusted up to level which provides aninner primary coating having a fiber friction and crack propagation thatare suitable for ribbon stripping. For example, the molecular weight ofthe polymeric block can be adjusted upward to level which provides aninner primary coating having a combination of fiber friction and crackpropagation that provides a predicted strip cleanliness of about 3 orless, and preferably about 2 or less. Alternatively, the molecularweight of the polymeric block can be adjusted upward to level whichprovides an inner primary coating having a fiber friction of about 30g/mm or less at a rate of 0.1 mm/sec in combination with a crackpropagation of at least about 1.3 mm at a rate of 0.1 mm/sec, at aribbon stripping temperature. Preferably, the fiber friction is about 25g/mm or less and more preferably about 20 g/mm or less. Preferably, thecrack propagation is at least about 1.5 mm and more preferably at leastabout 2 mm. The crack propagation is usually below about 4, but can behigher.

It has been found that by using polymeric blocks having a molecularweight greater than 2000, preferably at least about 2500, and mostpreferably at least about 3000, inner primary coatings having a fiberfriction and a crack propagation as described above can be provided. Themolecular weight of said polymeric block is usually less than about10,000, preferably less than about 8,000.

The coupling groups can be any group capable of providing a link betweenpolymer blocks and/or between radiation-curable functional groups andpolymer blocks. Examples of suitable coupling groups are urethane, ureaand thiourethane. For purposes of practicing the present invention,which relates to adjusting the crack propagation and fiber frictionusing the molecular weight of the polymeric blocks and/or urethaneconcentration, the following groups are not considered coupling groupswhen determining the molecular weight of the polymeric blocks:carbonate, ether, and ester groups. Thus, when determining the molecularweight of the polymeric block, ether groups, carbonate groups, and estergroups are considered part of the polymeric block. Polymeric compoundsseparated by urethane, thiourethane and urea groups are consideredseparate polymeric blocks. Urethane is the preferred coupling group.

Usually, urethane groups are used as the coupling groups in theradiation-curable oligomer. For example, if an oligomer having a numberaverage molecular weight about 6000 comprising 3 polymer blocks, eachhaving a number average molecular weight of about 2000, and containing 2radiation-curable functional groups, will have four urethane linkages.Two of the urethane linkages connect the radiation-curable groups to thepolymeric blocks and two of the urethane linkages connect the threepolymeric blocks together.

It has now been found that as the concentration of urethane linkagespresent in the inner primary composition is decreased, the crackpropagation of the inner primary coating increases and the fiberfriction of the inner primary coating decreases. Thus, the term urethaneconcentration represents the weight percentage of all urethane linkagespresent in the inner primary coating composition, based on the totalweight. of the inner primary coating composition.

Based on this discovery, the urethane concentration should be adjusteddownward to a level which provides an inner primary coating having afiber friction and crack propagation that are suitable for ribbonstripping the desired ribbon assembly. For example, the urethaneconcentration can be adjusted downward to a level which provides aninner primary coating having a combination of fiber friction and crackpropagation that provides a predicted strip cleanliness of about 3 orless, and preferably about 2 or less. It has been found that if theconcentration of urethane linkages is about 4% by weight or less, innerprimary coatings having a fiber friction and a crack propagation thatexhibit a predicted strip cleanliness of about 3 or less can beprovided. Preferably, the urethane concentration is about 3.5% by weightor less, more preferably about 2.5% or less by weight, and mostpreferably about 2% or less by weight. The urethane concentration effecton fiber friction and crack propagation is more pronounced for highermolecular weight oligomers, such as about 3,000 to about 10,000, morepreferably about 3,500 to about 8,000. Thus, preferably the urethaneoligomer has a molecular weight of about 3,000 to about 10,000 incombination with a urethane concentration of about 4% by weight or less,more preferably, a molecular of about 3,500 to about 8,000 incombination with a urethane concentration of about 3.5% or less, andmost preferably, a molecular weight of about 3,500 to about 8,000 incombination with a urethane concentration of about 3% or less.

The polymeric blocks can comprise for example polyethers, polyolefins,polycarbonates, polyesters, polyamides or copolymers thereof.Preferably, the polymeric blocks comprise polyethers.

The radiation-curable functional groups used can be any functional groupcapable of polymerization when exposed to actinic radiation. Suitableradiation-curable functional groups are now well known and within theskill of the art.

Commonly, the radiation-curable functionality used is ethylenicunsaturation, which can be polymerized through radical polymerization orcationic polymerization. Specific examples of suitable ethylenicunsaturation are groups containing acrylate, methacrylate, styrene,vinylether, vinyl ester, N-substituted acrylamide, N-vinyl amide,maleate esters, and fumarate esters. Preferably, the ethylenicunsaturation is provided by a group containing acrylate, methacrylate,or styrene functionality, and most preferably acrylate or methacrylate.

Another type of radiation-curable functionality generally used isprovided by, for example, epoxy groups, or thiol-ene or amine-enesystems. Epoxy groups can be polymerized through cationicpolymerization, whereas the thiol-ene and amine-ene systems are usuallypolymerized through radical polymerization. The epoxy groups can be, forexample, homopolymerized. In the thiol-ene and amine-ene systems, forexample, polymerization can occur between a group containing allylicunsaturation and a group containing a tertiary amine or thiol.

The radiation-curable oligomer can be easily formed by reacting apolymeric polyol, a compound containing a radiation-curable functionalgroup and a hydroxyl group, and a polyisocyanate. The general reactionof isocyanate functional groups with hydroxyl groups to form urethanelinkages is well known in the art. Thus, one skilled in the art will beable to make the improved oligomer according to the present inventionbased on the disclosure provided herein.

Examples of suitable polymeric polyols that can be used to form theradiation-curable oligomer include polyether diols, polyolefin diols,polyester diols, polycarbonate diols, and mixtures thereof. Polyetherand polycarbonate diols, or combinations thereof, are preferred. Thepolymeric block is the residue of the polymeric polyol after reaction toform the radiation-curable oligomer.

If a-polyether diol is used, preferably the polyether is a substantiallynon-crystalline polyether. Preferably, the polyether comprises repeatingunits of one or more of the following monomer groups:

Thus, suitable polyethers can be made from epoxy-ethane, epoxy-propane,tetrahydrofuran, methyl-substituted tetrahydrofuran, epoxybutane, andthe like. Commercial examples of a suitable polyether polyols that canbe used are PTGL2500, PTGL3000, PTGL3500, and PTGL4000 (HodogayaChemical Company).

If a polyolefin diol is used, the polyolefin is preferably a linear orbranched hydrocarbon containing a plurality of hydroxyl end groups. Thehydrocarbon provides a hydrocarbon backbone for the oligomer.Preferably, the hydrocarbon is a non-aromatic compound containing amajority of methylene groups (—CH₂—) and which can contain internalunsaturation and/or pendent unsaturation. Examples of suitablehydrocarbon diols include, for example: hydroxyl-terminated;

fully or partially hydrogenated 1,2-polybutadiene; copolymers of1,4-polybutadiene;

copolymers of 1,2-polybutadiene;

polyisobutylene polyol;

mixtures thereof, and the like. Preferably, the hydrocarbon diol is asubstantially, fully hydrogenated 1,2-polybutadiene-ethene copolymer or1,2-polybutadiene-ethene copolymer.

Examples of polycarbonate diols are those conventionally produced by thealcoholysis of diethylene carbonate with a diol.

Examples of polyester diols include the reaction products of saturatedpolycarboxylic acids, or their anhydrides, and diols. Commercialexamples are the polycaprolactones, commercially available from UnionCarbide under the trade designation Tone Polylol series of products, forexample, Tone 0200, 0221, 0301, 0310, 2201, and 2221. Tone Polyol 0301and 0310 are trifunctional.

Any organic polyisocyanate, alone or in admixture, can be used as thepolyisocyanate. Examples of suitable diisocyanates include: isophoronediisocyanate (IPDI);

toluene diisocyanate (TDI);

diphenylmethylene diisocyanate;

hexamethylene diisocyanate;

cyclohexylene diisocyanate;

methylene dicyclohexane diisocyanate;

2,2,4-trimethyl hexamethylene diisocyanate;

m-phenylene diisocyanate;

4-chloro-1,3-phenylene diisocyanate;

4,4′-biphenylene diisocyanate;

1,5-naphthylene diisocyanate;

1,4-tetramethylene diisocyanate;

1,6-hexamethylene diisocyanate;

1,10-decamethylene diisocyanate;. 1,4-cyclohexylene diisocyanate; and

polyalkyloxide and polyester glycol diisocyanates such aspolytetramethylene ether glycol terminated with TDI and polyethyleneadipate terminated with TDI, respectively. Preferably, the isocyanatesare TDI or IPDI.

If other oligomers, monomers, and/or additives containing urethanelinkages are used in admixture with the above describedradiation-curable oligomer to form an inner primary composition, theconcentration of urethane linkages present in each other oligomer,monomer or additive should be included in the urethane concentrationcalculation. Examples of common monomers containing urethane linkagesinclude:

trimethyl-olpropane triacrylate,

the triacrylate or methacrylate from hexane-2,4,6 triol, or fromglycerol, ethoxylated glycerol, or propoxylated glycerol,

hexanediol diacrylate,

1,3-butylene glycol diacrylate,

neopentyl glycol diacrylate,

1,6-hexanediol diacrylate,

neopentyl glycol diacrylate,

polyethylene glycol-200 diacrylate,

tetraethylene glycol diacrylate,

triethylene glycol diacrylate,

pentaerythritol tetraacrylate,

tripropylene glycol diacrylate,

ethoxylated bisphenol-A diacrylate,

trimetylolpropane diacrylate,

di-trimethylolpropane tetraacrylate,

triacrylate of tris(hydroxyethyl)isocyanurate,

dipentaerythritol hydroxypentaacrylate,

pentaerythritoltriacrylate,

ethoxylated trimethylolpropane triacrylate,

triethylene glycol dimethacrylate,

ethylene glycol dimethacrylate,

tetraethylene glycol dimethacrylate,

polyethylene glycol-2000 dimethacrylate,

1,6-hexanediol dimethacrylate,

neopentyl glycol dimethacrylate,

polyethylene glycol-600 dimethacrylate,

1,3-butylene glycol dimethacrylate,

ethoxylated bisphenol-A dimethacrylate, trimethylolpropanetrimethacrylate,

diethylene glycol dimethacrylate,

1,4-butanediol diacrylate,

diethylene glycol dimethacrylate,

pentaerythritol tetramethacrylate,

glycerin dimethacrylate,

trimethylolpropane dimethacrylate,

pentaerythritol trimethacrylate,

pentaerythritol dimethacrylate,

pentaerythritol diacrylate, and the like and mixtures thereof.

Mono(meth)acrylates such as cyclohexyl(meth)acrylate,

isobornyl(meth)acrylate,

lauryl(meth)acrylate,

alkoxylated phenolacrylate,

isooctyl-acrylate,

2-ethylhexyl-acrylate,

hydroxyethyl acrylate, and

tetrahydrofurfuryl(meth)-acrylate.

The Invention will be further explained by the following non-limitingexamples illustrating the use of block polymeric formulations.

EXAMPLES 10-1 THROUGH 10-14 Comparative Examples J-1 through J-11

Inner primary compositions were made by combining the components shownin Tables 15 and 16, in the same manner as described herein above. Theviscosity of the compositions was measured as described above, and theresults are shown in Tables 15 and 16. The inner primary compositionswere cured by exposure to UV radiation and the fiber friction and crackpropagation properties were measured, in the same manner as describedherein above. The test results are shown in Tables 15 and 16.

TABLE 15 Ex. Ex. Ex. Ex. Ex. Ex. Ex. 10-1 10-2 10-3 10-4 10-5 10-6 10-7Component (% by weight of total composition) Oligomer H-I-PPG3025-I-H49.38 0 0 0 0 0 0 Oligomer H-I-PPG4025-I-H 0 49.38 0 0 0 0 0 OligomerH-I-PTGL3000-I-H 0 0 64.38 0 0 49.38 0 Oligomer H-I-PTGL3500-I-H 0 0 064.38 0 0 49.38 Oligomer H-I-PTGL4000-I-H 0 0 0 0 64.38 0 0 OligomerH-(I-PTGL2000)₂- 0 0 0 0 0 0 0 I-H Phenoxy Ethyl Acrylate 0 0 0 0 0 0 0Ethoxylated Nonylphenol 40.32 40.32 25.32 25.32 25.32 40.32 40.32Acrylate Ester Isobornyl Acrylate 0 0 0 0 0 0 0 Lauryl Acrylate 6 6 6 66 6 6 Thiodiethylene bis (3,5-di- .3 .3 .3 .3 .3 .3 .3tert-butyl-4-Hydroxy) Hydrocinnamate 2,4,6-Trimethylbenzoyl 3 3 3 3 3 33 Diphenyl Phosphine Oxide and 2-Hydroxy-2-Methyl-1- Phenyl-1-Propanone2-Hydroxy-2-Methyl-1- 0 0 0 0 0 0 0 Phenyl-1-Propanone Bis(2,6-Dimethoxybenzyl) (2,4,4-Trimethylpentyl) Phosphine Oxidegamma-Mercaptopropyl 1 1 1 1 1 1 1 Trimethoxy Silane Test ResultsViscosity mPa · s (25 C.) 1200 1190 25350 321350 16840 9380 17680Urethane Concentration 2.01 1.76 2.99 2.65 2.24 2.29 2.03 (%)¹ FiberPull-Out Friction 19.3 10.8 23.23 21.27 27.63 21.84 14.04 (g/mm) CrackPropagation (mm) 1.5 2.18 1.66 1.63 1.82 1.76 2.32 Ex. Ex. Ex. Ex. Ex.Ex. Ex. 10-8 10-9 10-10 10-11 10-12 10-13 10-14 Component (% by weightof total composition) Oligomer H-I-PPG3025-I-H 0 0 0 0 0 0 0 OligomerH-I-PPG4025-I-H 0 0 0 0 0 0 0 Oligomer H-I-PTGL3000-I-H 0 0 0 0 0 0 0Oligomer H-I-PTGL3500-I-H 0 0 39.38 45.23 45.23 65.33 64.68 OligomerH-I-PTGL4000-I-H 49.38 0 0 0 0 0 0 Oligomer H-(I-PTGL2000)₂- 0 50.5 0 00 0 0 I-H 4 Phenoxy Ethyl Acrylate 0 14 0 25.13 20.1 20.1 17.91Ethoxylated Nonylphenol 40.32 15.1 50.21 25.13 20.1 0 0 Acrylate Ester 6Isobornyl Acrylate 0 10 0 0 10.5 10.5 6.97 Lauryl Acrylate 6 6 5.99 0 00 5.97 Thiodiethylene bis (3,5-di- .3 .3 .3 .3 .3 .3 .3tert-butyl-4-Hydroxy) Hydrocinnamate 2,4,6-Trimethylbenzoyl 3 0 0 0 0 00 Diphenyl Phosphine Oxide and 2-Hydroxy-2-Methyl-1- Phenyl-1-Propanone2-Hydroxy-2-Methyl-1- 0 3 3 3 3 3 3 Phenyl-1-PropanoneBis(2,6-Dimethoxybenzyl) (2,4,4-Trimethylpentyl) Phosphine Oxidegamma-Mercaptopropyl 1 1 1 1 1 1 Trimethoxy Silane Test ResultsViscosity mPa · s (25 C.) 7050 5570 4530 7220 5540 10670 9440 UrethaneConcentration 1.72 2.67 1.62 1.86 1.86 2.69 2.66 (%)¹ Fiber Pull-OutFriction 16.15 25.3 13.4 15.8 15.2 25.6 21.6 (g/mm) Crack Propagation(mm) 2.31 2.04 2.6 2 2.9 1.6 1.8 ¹The urethane concentration can becalculated from (1) the amount of NCO present in the urethane linkagesof the oligomer, (2) the molecular weight of the oligomer, which can bemeasured by conventional methods, and (3) the amount of oligomer in thecomposition. The polyol molecular weights in Table I are estimatedrather than measured molecular weights.

TABLE 16 Comp. Comp Comp Comp Comp Comp Comp Comp Comp Comp. Comp. Ex.Ex. Ex. Ex. Ex. Ex. Ex. Ex. Ex. Ex. Ex. J-1 J-2 J-3 J-4 J-5 J-6 J-7 J-8J-9 J-10 J-11 Component (% by weight based on total weight ofcomposition) Oligomer H-I-PTGL2000-I-H 0 83.7 68.7 79.7 79.7 74.7 69.767.7 79.7 49.38 64.38 Oligomer H-(I-PERM1000)_(1.4)- 56 0 0 0 0 0 0 0 00 0 (I-PPG1025)_(1.06)-I-H isodecyl acrylate 14 HI 0 0 0 0 0 5 10 15 0 00 Phenoxy Ethyl Acrylate 0 0 5 0 10 10 7 0 0 0 Ethoxylated NonylphenolAcrylate Ester 25.5 6 21 0 0 0 0 0 0 40.32 25.32 Isobornyl Acrylate 0 00 5 10 0 0 0 10 0 0 Lauryl Acrylate 0 6 6 6 6 6 6 6 6 6 6 Thiodiethylenebis (3,5-di-tert-butyl-4- .5 .3 .3 .3 .3 .3 .3 .3 .3 .3 .3 Hydroxy)Hydrocinnamate 2,4,6-Trimethylbenzoyl Diphenyl 0 3 3 3 3 3 3 3 0 3 3Phosphine Oxide and 2-Hydroxy-2- Methyl-1-Phenyl-1-Propanone2-Hydroxy-2-Methyl-1-Phenyl-1- 3 0 0 3 3 3 3 3 3 0 0 Propanone Bis(2,6-Dimethoxybenzyl) (2,4,4-Trimethylpentyl) Phosphine Oxidegamma-Mercaptopropyl Trimethoxy 1 1 1 1 1 1 1 1 1 1 1 Silane TestResults Viscosity mPa · s (25 C.) 6000 5050 10310 Urethane Concentration(%) 4.9 5.38 4.42 5.12 5.12 5.31 5.49 5.87 5.12 3.53 4.30 Fiber Pull-OutFriction (g/mm) 44 41.97 34.84 41.8 40.2 44.6 40.4 39.9 44.9 34.84 41.17Crack Propagation (mm) 1 1.32 1.45 1.21 1.25 1.05 1.2 1.17 1.2 1.45 1.32The oligomers in Tables 15 and 16 were formulated from the followingcomponents: H = Hydroxyethylacrylate I = Isophoronediisocyanate HI =Hexane diisocyanate PTGL2000 =polymethyltetrahydrofurfuryl/polytetrahydrofurfuryl copolymer diolhaving the molecular weight of 2000 (Mitsui, NY) PPG1025 =polypropyleneoxide diol having an average molecular weight of 1025,(BASF) Perm 1000 = Permanol KM10-1733 polycarbonate/polyether copolymerdiol having an average molecular weight of 1000

As can be seen from Examples 10-6 through 10-8, and Comparative ExampleJ-10, as the concentration of urethane decreases, the crack propagationincreases and the fiber friction decreases. Furthermore, as themolecular weight of the polymeric blocks increases, the crackpropagation increases and the fiber friction decreases.

Similarly, as can be seen from Examples 10-3 through 10-5, andComparative Example J-11, as the concentration of urethane decreases,the crack propagation increases and the fiber friction decreases.Furthermore, as the molecular weight of the polymeric blocks increases,the crack propagation increases and the fiber friction decreases.Examples 10-3 through 10-5 used significantly more of theradiation-curable oligomer than Examples 10-6 through 10-8, and the sametrend in fiber friction and crack propagation was clearly demonstrated.Based on this experimental evidence, the trend in fiber friction andcrack propagation is dependent mainly upon the oligomer. Furthermore,these Examples used a polyether polymeric block.

Examples 10-1 and 10-2 demonstrate that when a polypropylene oxidepolymeric block is used as a polyether polymeric block, the crackpropagation and fiber friction are still dependent upon the molecularweight of the polymeric block and/or the concentration of urethane ifused. In particular, as the concentration of urethane decreases, thecrack propagation increases and the fiber friction decreases.Furthermore, as the molecular weight of the polymeric blocks increases,the crack propagation increases and the fiber friction decreases.

Examples 10-4, 10-7 and 10-10 through 10-14 used different amounts ofthe same radiation-curable oligomer. The experimental resultsdemonstrate that the trend in crack propagation and fiber friction isbased on the molecular weight of the polymeric block and/or theconcentration of urethane.

The test results in Table 15 demonstrate that the above. describedtrends regarding crack propagation and fiber friction based on molecularweight and/or urethane concentration are independent of the type ofoligomers and is generally consistent among the different types ofoligomers.

FIG. 7 illustrates a graph which includes the data shown in Tables 15and 16, above. As can be seen from FIG. 7, the urethane concentration inthe inner primary composition directly affects the fiber pull-outfriction. As the urethane concentration is decreased, the fiber pull-outfriction is decreased.

FIG. 8 illustrates a graph of the fiber friction versus urethaneconcentration for Examples 10-10 through 10-14. FIG. 8 clearlydemonstrates the direct correlation between fiber pull-out friction andurethane concentration in the inner primary composition. In particular,as the urethane concentration decreases the fiber pull-out frictiondecreases.

EXAMPLES 10-15 THROUGH 10-22

Inner primary compositions were made by combining the components shownin Table 17, in the same manner as described herein above. The viscosityof the compositions was measured as described above, and the results areshown in Table 17. The inner primary compositions were cured by exposureto UV radiation and the fiber friction and crack propagation propertieswere measured, in the same manner as described herein above. The testresults are shown in Table 17.

TABLE 17 Exmp. Exmp. Exmp. Exmp. Exmp. Exmp. Exmp. Exmp. 10-15 10-1610-17 10-18 10-19 10-20 10-21 10-22 Component (% by weight based ontotal weight of composition) Oligomer H-(I-PTGL2000)₂-I-H 23.71 28.4533.19 37.93 42.68 47.42 52.16 56.9 Phenoxy Ethyl Acrylate 64.68 58.5252.35 46.19 40.03 33.86 27.7 21.53 Ethoxylated Nonylphenol AcrylateEster 7.11 8.53 9.95 11.38 12.87 14.22 15.64 17.06 Thiodiethylene bis(3,5-di-tert-butyl-4- 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 Hydroxy)Hydrocinnamate 2-Hydroxy-2-Methyl-1-Phenyl-1-Propanone 3 3 3 3 3 3 3 3Bis (2,6-Dimethoxybenzyl) (2,4,4- Trimethylpentyl) Phosphine Oxidegamma-Mercaptopropyl Trimethoxy Silane 1 1 1 1 1 1 1 1 Test ResultsViscosity mPa · s (25 C.) 430 730 1200 2000 3270 5070 8500 14,500Urethane Concentration (%) 1.25 1.5 1.75 2 2.25 2.5 2.75 3 FiberPull-Out Friction (g/mm) 20.5 22.7 23.9 28.7 26.4 35.2 31.8 40.1 CrackPropagation (mm) 2.31 2.32 1.96 1.89 1.8 1.77 1.75 1.51 The oligomers inTable 17 were formulated from the following components: H =Hydroxyethylacrylate I = Isophoronediisocyanate PTGL 2000 =polymethyltetrahydrofurfuryl/polytetrahydrofurfuryl copolymer diolhaving an average molecular weight of 2000, (Mitsui, NY)

FIG. 9 illustrates a graph of the experimental results of Examples 10-15through 10-22. As can be seen from FIG. 9, as the urethane concentrationdecreases the fiber pull-out friction decreases.

EXAMPLES 10-22A THROUGH 10-24

Inner primary compositions were made by combining the components shownin Table 18, in the same manner as described herein above. The viscosityof the compositions was measured as described above, and the results areshown in Table 18. The inner primary compositions were cured by exposureto UV radiation and the fiber friction and crack propagation propertieswere measured, in the same manner as described herein above. The testresults are shown in Table 18.

TABLE 18 Example Example Example 10-22A 10-23 10-24 Component (% byweight based on total weight of composition) Oligomer H-I-PTGL4200-I-H 049.38 45.01 Oligomer 49.38 0 0 H-(I-PTGL2000)₂-I-H Monomer H-HI 0 0 8.85Ethoxylated Nonylphenol Acrylate 40.32 40.32 36.75 Ester Thiodiethylenebis(3,5-di-tert-butyl- 0.3 0.3 0.27 4-Hydroxy) Hydrocinnamate LaurylAcrylate 6 6 5.47 2-Hydroxy-2-Methyl-1-Phenyl-1- 3 3 2.73 Propanone Bis(2,6-Dimethoxy- benzyl) (2,4,4-Trimethylpentyl) Phosphine Oxidegamma-Mercaptopropyl Trimethoxy 1 1 .91 Silane Test Results ViscositymPa · s (25 C) 9260 7050 5100 Urethane Concentration (%) 2.61 1.72 2.61Fiber Pull-Out Friction (g/mm) 20.85 16.85 17.4 Crack Propagation (mm)1.62 2.06 1.74 The oligomers and monomers in Table 18 were formulatedfrom the following components: H = Hydroxyethylacrylate I =Isophoronediisocyanate HI = Hexane isocyanate PTGL 4200 =polymethyltetrahydrofurfuryl/polytetrahydrofurfuryl copolymer diolhaving an average molecular weight of 4200, (Mitsui, NY) PTGL 2000 =polymethyltetrahydrofurfuryl/polytetrahydrofurfuryl copolymer diolhaving an average molecular weight of 2000, (Mitsui, NY)

By comparing Example 10-22A with 10-24, it becomes clear that by using ahigher molecular weight polymeric block, 4200 g/mole in Example 10-24compared to 2000 g/mole in Example 10-22A, the fiber friction can besignificantly decreased and the crack propagation can be increased. Theurethane concentration was the same for both Examples 10-22A and 10-24.The oligomer used contained a polyether backbone.

EXAMPLES 10-25 THROUGH 10-28

Inner primary compositions were made by combining the components shownin Table 19, in the same manner as described herein above. The viscosityof the compositions was measured as described above, and the results areshown in Table 19. The inner primary compositions were cured by exposureto UV radiation and the fiber friction and crack propagation propertieswere measured, in the same manner as described herein above. The testresults are shown in Table 19.

TABLE 19 Ex. Ex. Ex. Ex. 10-25 10-26 10-27 10-28 Component (% by weightbased on total weight of composition) Oligomer 50 45 40 35H-I-(NissoPB2000)₂-I-H Ethoxylated Nonylphenol Acrylate 29.5 34.5 39.544.5 Ester Isobornyl Acrylate 10 10 10 10 Thiodiethylenebis(3,5-di-tert- 0.5 0.5 0.5 0.5 butyl-4-Hydroxy) Hydrocinnamate LaurylAcrylate 6 6 6 6 2-Hydroxy-2-Methyl-1-Phenyl-1- 3 3 3 3 PropanoneBis(2,6-Dimethoxy- benzyl) (2,4,4-Trimethylpentyl) Phosphine Oxidegamma-Mercaptopropyl 1 1 1 1 Trimethoxy Silane Test Results ViscositymPa · s (25 C) Urethane Concentration (%) 2.64 2.37 2.11 1.84 FiberPull-Out Friction (g/mm) 13.88 13.49 9.24 6.94 Crack Propagation (mm)1.79 1.52 * * The oligomers and monomers in Table 19 were formulatedfrom the following components: H = Hydroxyethylacrylate I =Isophoronediisocyanate NissoPB 2000 = Polybutadiene copolymer diolhaving an average molecular weight of 2000, (Nippon Soda) *The crackpropagation could not be measured for these two coatings.

FIG. 10 illustrates a graph of the experimental results of Examples10-25 through 10-28. As can be seen from FIG. 10, as the urethaneconcentration decreases the fiber pull-out friction decreases. Theoligomer used contained a polyolefin backbone.

EXAMPLES 10-29 THROUGH 10-32

Inner primary compositions were made by combining the components shownin Table 20 in the same manner as described herein above. The viscosityof the compositions was measured as described above, and the results areshown in Table 20. The inner primary compositions were cured by exposureto UV radiation and the fiber friction and crack propagation propertieswere measured, in the same manner as described herein above. The testresults are shown in Table 20.

TABLE 20 Ex. Ex. Ex. Ex. 10-29 10-30 10-31 10-32 Component (% by weightbased on total weight of composition) Oligomer H-I-PTGL2000-I-H 40 40 4040 H-BI 0 4.24 9.18 14.12 Ethoxylated Nonylphenol Acrylate 10 10 10 10Ester Phenoxyethyl Acrylate 45.5 41.26 36.32 31.38 Thiodiethylenebis(3,5-di-tert- 0.5 0.5 0.5 0.5 butyl-4-Hydroxy) Hydrocinnamate2-Hydroxy-2-Methyl-1-Phenyl-1- 3 3 3 3 Propanone Bis(2,6-Dimethoxy-benzyl) (2,4,4-Trimethylpentyl) Phosphine Oxide gamma-Mercaptopropyl 1 11 1 Trimethoxy Silane Test Results Viscosity mPa · s (25 C) 770 810 870950 Urethane Concentration (%) 2.5 3 3.5 4 Fiber Pull-Out Friction(g/mm) 39.1 40.4 42.7 47.9 Crack Propagation (mm) 1.27 1.24 1.28 1.13The oligomers and monomers in Table 20 were formulated from thefollowing components: H = Hydroxyethyl Acrylate I = IsophoroneDiisocyanate BI = Butyl Isocyanate

FIG. 11 illustrates a graph of the experimental results of Examples10-29 through 10-32. As can be seen from FIG. 11, as the urethaneconcentration decreases the fiber pull-out friction decreases.

EXAMPLES 10-33 THROUGH 10-36

Inner primary compositions were made by combining the components shownin Table 21, in the same manner as described herein above. The viscosityof the compositions was measured as described above, and the results areshown in Table 21. The inner primary compositions were cured by exposureto UV radiation and the fiber friction and crack propagation propertieswere measured, in the same manner as described herein above. The testresults are shown in Table 21.

TABLE 21 Ex. 10-33 Ex. 10-34 Ex. 10-35 Ex. 10-36 Comp. Ex. J-1 Component(% by weight based on total weight of composition) OligomerH-I-PPG2025-I-Perm2000-I-H 50 45 40 35 0 Oligomer 0 0 0 0 70H-I-(PPG2025)_(1.4)-I-(Perm1000)_(1.06)-I-H Ethoxylated NonylphenolAcrylate Ester 10 10 10 10 25.5 Lauryl Acrylate 6 6 6 6 0 Thiodiethylenebis (3,5-di-tert-butyl-4- 0.5 0.5 0.5 0.5 0.5 Hydroxy) Hydrocinnamate2-Hydroxy-2-Methyl-1-Phenyl-1-Propanone 1.5 1.5 1.5 1.5 3 Bis(2,6-Dimethoxybenzyl) (2,4,4- Trimethylpentyl) Phosphine Oxidegamma-Mercaptopropyl Trimethoxy Silane 1 1 1 1 1 Test Results ViscositymPa · s (25 C.) 6000 Urethane Concentration (%) 2.03 1.83 1.62 1.42 4.9Fiber Pull-Out Friction (g/mm) 11.87 11.5 9.9 9.8 44 Crack Propagation(mm) 0 3.3 3.2 3.1 1 The oligomers and monomers in Table 21 wereformulated from the following components: H = Hydroxyethyl Acrylate I =Isophorone Diisocyanate Perm 1000 = Permanol KM10-1733polycarbonate/polyether copolymer diol having an average molecularweight of 1000 PPG2025 = PC1122 a polycarbonate/polyether copolymer diolhaving an average molecular weight of 2000

The test results in Table 21 illustrate that as the urethaneconcentration decreases the fiber pull-out friction decreases and thecrack propagation increases. The test results in Table 21 alsoillustrate that as the molecular weight of the polymeric block increasesthe fiber pull-out friction decreases and the crack propagationincreases. The polymeric block used was a polycarbonate.

Ribbon Assemblies

Ribbon assemblies are now well known in the art and one skilled in theart will readily be able to use the disclosure provided herein toprepare the novel ribbon assemblies having enhanced ribbon strippabilityfor the desired applications. The novel ribbon assembly made accordingto this invention can be advantageously used in varioustelecommunication systems. Such telecommunication systems typicallyinclude ribbon assemblies containing optical glass fibers, incombination with transmitters, receivers, and switches. The ribbonassemblies containing the coated optical glass fibers are thefundamental connecting units of telecommunication systems. The ribbonassembly can be buried under ground or water for long distanceconnections, such as between cities. The ribbon assembly can also beused to connect directly to residential homes.

The novel ribbon assembly made according to this invention can also beused in cable television systems. Such cable television systemstypically include ribbon assemblies containing optical glass fibers,transmitters, receivers, and switches. The ribbon assemblies containingthe coated optical glass fibers are the fundamental connecting units ofsuch cable television systems. The ribbon assembly can be buried underground or water for long distance connections, such as between cities.The ribbon assembly can also be used to connect directly to residentialhomes.

The novel ribbon assemblies can also be used in a wide variety oftechnologies, including but not limited to, various security systems,data transmission lines, high density television, and computer appliancesystems. It will be appreciated that as a result of the fundamentaldiscoveries described herein including the relationship between thefiber friction forces and the cohesive strength of the coatingsthemselves, and the means to control and establish such features andfunctions, the optical fiber art is now able to realize significantadvantages. These are primarily exhibited, as explained above, in thestripping and cable splicing function, but those operations arenonetheless critical in the establishment of a ribbon/cable network ofcommunication.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to those of ordinaryskill in the art that various changes and modifications can be made tothe claimed invention without departing from the spirit and scopethereof. For instance, while this invention has principally beendescribed with reference to ribbon constructions and assemblies ofoptical fibers, it is equally adaptable to other geometric andstructural arrays of multiple fiber conduits and cables.

Accordingly, applicants believe that the scope of this invention isdefined solely by the terminology set forth in the following claims andis not otherwise limited.

What is claimed is:
 1. A composition for coating an optical fiber, saidcomposition comprising a polyester oligomer having at least onefunctional group capable of polymerizing under the influence ofradiation, said composition after radiation cure having the combinationof properties of: (a) a fiber pull-out friction of less than 40 g/mm at90° C.; (b) a crack propagation of greater than 1.0 mm at 90° C.; (c) aglass transition temperature of −10° C. or less; and (d) sufficientadhesion to said fiber to prevent delamination in the presence ofmoisture and during handling.
 2. A coated optical fiber comprising atleast an inner primary coating and an outer primary coating, whereinsaid inner primary coating is obtained by curing the composition ofclaim
 1. 3. A ribbon assembly comprising: (i) a plurality of coatedoptical fibers, at least one of said coated optical fibers being thecoated optical fiber of claim 2, and (ii) a matrix material bonding saidplurality of coated optical fibers together.
 4. The composition of claim1, wherein said oligomer comprises a polyether polyol residue.
 5. Thecoated optical fiber of claim 2, wherein said oligomer comprises apolyether polyol residue.
 6. The ribbon assembly of claim 3, whereinsaid oligomer comprises a polyether polyol residue.
 7. The compositionof claim 1, further comprising gamma-mercaptopropyl trimethoxysilane. 8.The coated optical fiber of claim 2, wherein said composition furthercomprises gamma-mercaptopropyl trimethoxysilane.
 9. The ribbon assemblyof claim 3, wherein said composition further comprisesgamma-mercaptopropyl trimethoxysilane.
 10. The coated optical fiber ofclaim 2, wherein the ratio of the change in length of said inner primarycoating to the change in length of said outer primary coating is lessthan 2 when said coatings are heated from 25° C. to strippingtemperature.
 11. The ribbon assembly of claim 3, wherein the ratio ofthe change in length of said inner primary coating to the change inlength of said outer primary coating is less than 2 when said coatingsare heated from 25° C. to stripping temperature.
 12. A composition forcoating an optical fiber, said composition comprising a fluorinatedoligomer having at least one functional group capable of polymerizingunder the influence of radiation, said composition after radiation curehaving the combination of properties of: (a) a fiber pull-out frictionof less than 40 g/mm at 90° C.; (b) a crack propagation of greater than1.0 mm at 90° C.; (c) a glass transition temperature of 10° C. or less;and (d) sufficient adhesion to said fiber to prevent delamination in thepresence of moisture and during handling.
 13. A coated optical fibercomprising at least an inner primary coating and an outer primarycoating, wherein said inner primary coating is obtained by curing thecomposition of claim
 12. 14. A ribbon assembly comprising: (i) aplurality of coated optical fibers, at least one of said coated opticalfibers being the coated optical fiber of claim 13; and (ii) a matrixmaterial bonding said plurality of coated optical fibers together. 15.The composition of claim 12, wherein said oligomer is obtained byreacting a fluorinated compound having hydroxyl functionality with adiisocyanate and hydroxyethylacrylate.
 16. The coated optical fiber ofclaim 13, wherein said oligomer is obtained by reacting a fluorinatedcompound having hydroxyl functionality with a diisocyanate andhydroxyethylacrylate.
 17. The ribbon assembly of claim 14, wherein saidoligomer is obtained by reacting a fluorinated compound having hydroxylfunctionality with a diisocyanate and hydroxyethylacrylate.
 18. Thecomposition of claim 12, further comprising gamma-mercaptopropyltrimethoxysilane.
 19. The coated optical fiber of claim 13, wherein saidcomposition further comprises gamma-mercaptopropyl trimethoxysilane. 20.The ribbon assembly of claim 14, wherein said composition furthercomprises gamma-mercaptopropyl trimethoxysilane.
 21. The composition ofclaim 12, wherein said glass transition temperature is −10° C. or less.22. The coated optical fiber of claim 13, wherein said glass transitiontemperature is −10° C. or less.
 23. The ribbon assembly of claim 14,wherein said glass transition temperature is −10° C. or less.
 24. Thecoated optical fiber of claim 13, wherein the ratio of the change inlength of said inner primary coating to the change in length of saidouter primary coating is less than 2 when said coatings are heated from25° C. to stripping temperature.
 25. The ribbon assembly of claim 14,wherein the ratio of the change in length of said inner primary coatingto the change in length of said outer primary coating is less than 2when said coatings are heated from 25° C. to stripping temperature.